Topics
>
Geometry>
Trigonometry>
Law of Sines: Solving for an Angle>
Law of Sines: Solving for an AngleLaw of Sines: Solving for an Angle
Try VividMath Premium to unlock full access
Time limit: 0
Quiz summary
0 of 5 questions completed
Questions:
- 1
- 2
- 3
- 4
- 5
Information
–
You have already completed the quiz before. Hence you can not start it again.
Quiz is loading...
You must sign in or sign up to start the quiz.
You have to finish following quiz, to start this quiz:
Loading...
- 1
- 2
- 3
- 4
- 5
- Answered
- Review
-
Question 1 of 5
1. Question
Find `theta`
Round your answer to the nearest minute- `theta=` (67)`°` (32)`'`
Hint
Help VideoCorrect
Nice Job!
Incorrect
Sine Law
$$\frac{\color{#007DDC}{a}}{\sin\color{#007DDC}{A}}=\frac{\color{#00880A}{b}}{\sin\color{#00880A}{B}}=\frac{\color{#9a00c7}{c}}{\sin\color{#9a00c7}{C}}$$where:
`a` is the side opposite angle `A`
`b` is the side opposite angle `B`
`c` is the side opposite angle `C`When to use the Sine Law (for non-right angled triangles)
a) Given 2 sides and 1 angle to find the other angleorb) Given 2 angles 1 side to find the other sideCalculator Buttons to Use
`sin` `=` Sine function`cos` `=` Cosine function`tan` `=` Tangent functionDMS or `° ‘ ‘ ‘` `=` Degree/Minute/SecondShift or 2nd F or INV `=` Inverse function`=` `=` Equal functionDegree-to-Minute Conversion
`1` degree `=60` minutesMinute-to-Second Conversion
`1` minute `=60` secondsRounding Off to the Nearest Minute
If the seconds is greater than or equal to `30”`, round the minute up.
If the seconds is less than `30”`, round the minute down.First, label the triangle according to the Sine Law.
Substitute the three known values to the Sine Law to find the fourth missing value.From labelling the triangle, we know that the known values are those with labels `b, B, c` and `C`.`b=29 cm``B=theta``c=18 cm``C=35°`$$\frac{\color{#00880A}{b}}{\sin\color{#00880A}{B}}$$ `=` $$\frac{\color{#9a00c7}{c}}{\sin\color{#9a00c7}{C}}$$ $$\frac{\color{#00880A}{29}}{\sin\color{#00880A}{\theta}}$$ `=` $$\frac{\color{#9a00c7}{18}}{\sin\color{#9a00c7}{35°}}$$ Substitute the values `18timessintheta` `=` `29timessin35°` Cross multiply `18timessintheta``divide18` `=` `29timessin35°``divide18` Divide both sides by `18` `sintheta` `=` `(29timessin35°)/18` `sintheta` `=` `16.632717/18` Use the calculator to simplify `sintheta` `=` `0.9240954` `theta` `=` `sin^(-1)0.9240954` `sin` inverse Simplify this further by evaluating `sin^(-1)0.9240954` using the calculator:`1.` Press Shift or 2nd F (depending on your calculator)`2.` Press `sin``3.` Press `0.9240954``4.` Press `=`The result will be: `67.5323°`Round off the answer to the nearest minute.`theta` `=` `67.5323°` `=` `67°31’56”` Press DMS on your calculator `=` `67°32’` Round up since the seconds is greater than `30”` 
`67°32’` -
Question 2 of 5
2. Question
Find `theta`
Round your answer to the nearest degree- `theta=` (62)`°`
Hint
Help VideoCorrect
Keep Going!
Incorrect
Sine Law
$$\frac{\color{#007DDC}{a}}{\sin\color{#007DDC}{A}}=\frac{\color{#00880A}{b}}{\sin\color{#00880A}{B}}=\frac{\color{#9a00c7}{c}}{\sin\color{#9a00c7}{C}}$$where:
`a` is the side opposite angle `A`
`b` is the side opposite angle `B`
`c` is the side opposite angle `C`When to use the Sine Law (for non-right angled triangles)
a) Given 2 sides and 1 angle to find the other angleorb) Given 2 angles 1 side to find the other sideCalculator Buttons to Use
`sin` `=` Sine function`cos` `=` Cosine function`tan` `=` Tangent functionDMS or `° ‘ ‘ ‘` `=` Degree/Minute/SecondShift or 2nd F or INV `=` Inverse function`=` `=` Equal functionDegree-to-Minute Conversion
`1` degree `=60` minutesMinute-to-Second Conversion
`1` minute `=60` secondsRounding Off to the Nearest Minute
If the seconds is greater than or equal to `30”`, round the minute up.
If the seconds is less than `30”`, round the minute down.First, label the triangle according to the Sine Law.
Substitute the three known values to the Sine Law to find the fourth missing value.From labelling the triangle, we know that the known values are those with labels `p, P, r` and `R`.`p=92 m``P=24°``r=200 m``R=theta`$$\frac{\color{#007DDC}{p}}{\sin\color{#007DDC}{P}}$$ `=` $$\frac{\color{#9a00c7}{r}}{\sin\color{#9a00c7}{R}}$$ $$\frac{\color{#007DDC}{92}}{\sin\color{#007DDC}{24°}}$$ `=` $$\frac{\color{#9a00c7}{200}}{\sin\color{#9a00c7}{\theta}}$$ Substitute the values `92timessintheta` `=` `200timessin24°` Cross multiply `92timessintheta``divide92` `=` `200timessin24°``divide92` Divide both sides by `92` `sintheta` `=` `(200timessin24°)/92` `sintheta` `=` `81.34733/92` Use the calculator to simplify `sintheta` `=` `0.88421` `theta` `=` `sin^(-1)0.88421` `sin` inverse Simplify this further by evaluating `sin^(-1)0.88421` using the calculator:`1.` Press Shift or 2nd F (depending on your calculator)`2.` Press `sin``3.` Press `0.88421``4.` Press `=`The result will be: `62.15447°`Round off the answer to the nearest degree.`theta` `=` `62.15447°` `=` `62°9’16”` Press DMS on your calculator `=` `62°` Round down since the minutes is less than `30’` 
`62°` -
Question 3 of 5
3. Question
Find `theta`
Round your answer to the nearest degree- `theta=` (74)`°`
Hint
Help VideoCorrect
Excellent!
Incorrect
Sine Law
$$\frac{\color{#007DDC}{a}}{\sin\color{#007DDC}{A}}=\frac{\color{#00880A}{b}}{\sin\color{#00880A}{B}}=\frac{\color{#9a00c7}{c}}{\sin\color{#9a00c7}{C}}$$where:
`a` is the side opposite angle `A`
`b` is the side opposite angle `B`
`c` is the side opposite angle `C`When to use the Sine Law (for non-right angled triangles)
a) Given 2 sides and 1 angle to find the other angleorb) Given 2 angles 1 side to find the other sideCalculator Buttons to Use
`sin` `=` Sine function`cos` `=` Cosine function`tan` `=` Tangent functionDMS or `° ‘ ‘ ‘` `=` Degree/Minute/SecondShift or 2nd F or INV `=` Inverse function`=` `=` Equal functionDegree-to-Minute Conversion
`1` degree `=60` minutesMinute-to-Second Conversion
`1` minute `=60` secondsRounding Off to the Nearest Minute
If the seconds is greater than or equal to `30”`, round the minute up.
If the seconds is less than `30”`, round the minute down.Since the values given are opposite each other, we can directly substitute them to the Sine Law.
`a=51.4 m``A=theta``b=52.9 m``B=82°`$$\frac{\color{#007DDC}{a}}{\sin\color{#007DDC}{A}}$$ `=` $$\frac{\color{#00880A}{b}}{\sin\color{#00880A}{B}}$$ $$\frac{\color{#007DDC}{51.4}}{\sin\color{#007DDC}{\theta}}$$ `=` $$\frac{\color{#00880A}{52.9}}{\sin\color{#00880A}{82°}}$$ Substitute the values `52.9timessintheta` `=` `51.4timessin82°` Cross multiply `52.9timessintheta``divide52.9` `=` `51.4timessin82°``divide52.9` Divide both sides by `52.9` `sintheta` `=` `(51.4timessin82°)/52.9` `sintheta` `=` `(51.4times0.990268)/52.9` Use the calculator to simplify `sintheta` `=` `50.8997787/52.9` `sintheta` `=` `0.9621886` `theta` `=` `sin^(-1)0.9621886` `sin` inverse Simplify this further by evaluating `sin^(-1)0.9621886` using the calculator:`1.` Press Shift or 2nd F (depending on your calculator)`2.` Press `sin``3.` Press `0.9621886``4.` Press `=`The result will be: `74.1938°`Round off the answer to the nearest degree.`theta` `=` `74.1938°` `=` `74°11’` Press DMS on your calculator `=` `74°` Round down since the minutes is less than `30’` 
`74°` -
Question 4 of 5
4. Question
Find the obtuse angle `alpha`
Round your answer to the nearest degree- `alpha=` (131)`°`
Hint
Help VideoCorrect
Excellent!
Incorrect
Sine Law
$$\frac{\color{#007DDC}{a}}{\sin\color{#007DDC}{A}}=\frac{\color{#00880A}{b}}{\sin\color{#00880A}{B}}=\frac{\color{#9a00c7}{c}}{\sin\color{#9a00c7}{C}}$$where:
`a` is the side opposite angle `A`
`b` is the side opposite angle `B`
`c` is the side opposite angle `C`When to use the Sine Law (for non-right angled triangles)
a) Given 2 sides and 1 angle to find the other angleorb) Given 2 angles 1 side to find the other sideCalculator Buttons to Use
`sin` `=` Sine function`cos` `=` Cosine function`tan` `=` Tangent functionDMS or `° ‘ ‘ ‘` `=` Degree/Minute/SecondShift or 2nd F or INV `=` Inverse function`=` `=` Equal functionDegree-to-Minute Conversion
`1` degree `=60` minutesMinute-to-Second Conversion
`1` minute `=60` secondsRounding Off to the Nearest Minute
If the seconds is greater than or equal to `30”`, round the minute up.
If the seconds is less than `30”`, round the minute down.Substitute the three known values to the Sine Law to find the fourth missing value.`a=37`m`A=alpha``b=16`m`B=19°`$$\frac{\color{#007DDC}{a}}{\sin\color{#007DDC}{A}}$$ `=` $$\frac{\color{#00880A}{b}}{\sin\color{#00880A}{B}}$$ $$\frac{\color{#007DDC}{37}}{\sin\color{#007DDC}{\alpha}}$$ `=` $$\frac{\color{#00880A}{16}}{\sin\color{#00880A}{19}}$$ Substitute the values `16timessinalpha` `=` `37timessin19°` Cross multiply `16timessinalpha``divide16` `=` `37timessin19°``divide16` Divide both sides by `16` `sinalpha` `=` `(37timessin19°)/16` `sinalpha` `=` `12.0460217/16` Use the calculator to simplify `sinalpha` `=` `0.75287636` `alpha` `=` `sin^(-1)0.75287636` `sin` inverse Simplify this further by evaluating `sin^(-1)0.75287636` using the calculator:`1.` Press Shift or 2nd F (depending on your calculator)`2.` Press `sin``3.` Press `0.75287636``4.` Press `=`The result will be: `48.8401549°`Round off the answer to the nearest degree.`alpha` `=` `48.8401549°` `=` `48°50’` Press DMS on your calculator `=` `49°` Round up since the minutes is greater than `30’` Notice that the result is an acute angle even though the actual angle is supposedly obtuse. This is because we used the Sine Law.To get the obtuse angle, simply subtract the angle from `180°`.`alpha` `=` `180-49` `alpha` `=` `131°` 
`131°` -
Question 5 of 5
5. Question
Find the obtuse angle `alpha`
Round your answer to the nearest degree- `alpha=` (150)`°`
Hint
Help VideoCorrect
Good Job!
Incorrect
Sine Law
$$\frac{\color{#007DDC}{a}}{\sin\color{#007DDC}{A}}=\frac{\color{#00880A}{b}}{\sin\color{#00880A}{B}}=\frac{\color{#9a00c7}{c}}{\sin\color{#9a00c7}{C}}$$where:
`a` is the side opposite angle `A`
`b` is the side opposite angle `B`
`c` is the side opposite angle `C`When to use the Sine Law (for non-right angled triangles)
a) Given 2 sides and 1 angle to find the other angleorb) Given 2 angles 1 side to find the other sideCalculator Buttons to Use
`sin` `=` Sine function`cos` `=` Cosine function`tan` `=` Tangent functionDMS or `° ‘ ‘ ‘` `=` Degree/Minute/SecondShift or 2nd F or INV `=` Inverse function`=` `=` Equal functionDegree-to-Minute Conversion
`1` degree `=60` minutesMinute-to-Second Conversion
`1` minute `=60` secondsRounding Off to the Nearest Minute
If the seconds is greater than or equal to `30”`, round the minute up.
If the seconds is less than `30”`, round the minute down.Substitute the three known values to the Sine Law to find the fourth missing value.`a=128`m`A=alpha``b=99`m`B=23°`$$\frac{\color{#007DDC}{a}}{\sin\color{#007DDC}{A}}$$ `=` $$\frac{\color{#00880A}{b}}{\sin\color{#00880A}{B}}$$ $$\frac{\color{#007DDC}{128}}{\sin\color{#007DDC}{\alpha}}$$ `=` $$\frac{\color{#00880A}{99}}{\sin\color{#00880A}{23}}$$ Substitute the values `99timessinalpha` `=` `128timessin23°` Cross multiply `99timessinalpha``divide99` `=` `128timessin23°``divide99` Divide both sides by `99` `sinalpha` `=` `(128timessin23°)/99` `sinalpha` `=` `50.013584/99` Use the calculator to simplify `sinalpha` `=` `0.5051877` `alpha` `=` `sin^(-1)0.5051877` `sin` inverse Simplify this further by evaluating `sin^(-1)0.5051877` using the calculator:`1.` Press Shift or 2nd F (depending on your calculator)`2.` Press `sin``3.` Press `0.5051877``4.` Press `=`The result will be: `30.343815°`Round off the answer to the nearest degree.`alpha` `=` `30.343815°` `=` `30°20’` Press DMS on your calculator `=` `30°` Round down since the minutes is less than `30’` Notice that the result is an acute angle even though the actual angle is supposedly obtuse. This is because we used the Sine Law.To get the obtuse angle, simply subtract the angle from `180°`.`alpha` `=` `180-30` `alpha` `=` `150°` 
`150°`
Quizzes
- Intro to Trigonometric Ratios (SOH CAH TOA) 1
- Intro to Trigonometric Ratios (SOH CAH TOA) 2
- Round Angles (Degrees, Minutes, Seconds)
- Evaluate Trig Expressions using a Calculator 1
- Evaluate Trig Expressions using a Calculator 2
- Trig Ratios: Solving for a Side 1
- Trig Ratios: Solving for a Side 2
- Trig Ratios: Solving for an Angle
- Angles of Elevation and Depression
- Trig Ratios Word Problems: Solving for a Side
- Trig Ratios Word Problems: Solving for an Angle
- Area of Non-Right Angled Triangles 1
- Area of Non-Right Angled Triangles 2
- Law of Sines: Solving for a Side
- Law of Sines: Solving for an Angle
- Law of Cosines: Solving for a Side
- Law of Cosines: Solving for an Angle
- Trigonometry Word Problems 1
- Trigonometry Word Problems 2
- Trigonometry Mixed Review: Part 1 (1)
- Trigonometry Mixed Review: Part 1 (2)
- Trigonometry Mixed Review: Part 1 (3)
- Trigonometry Mixed Review: Part 1 (4)
- Trigonometry Mixed Review: Part 2 (1)
- Trigonometry Mixed Review: Part 2 (2)
- Trigonometry Mixed Review: Part 2 (3)