Find cos⁡(a+b)\cos\left(a+b\right)cos(a+b) given cos⁡a=12\cos a=\frac12cosa=21, sin⁡b=12\sin b=\frac12sinb=21, & aaa is in Q IV and bbb is in Q II.

Table of contents

0. Review of College Algebra4h 43m
1. Measuring Angles39m
2. Trigonometric Functions on Right Triangles2h 5m
3. Unit Circle1h 19m
4. Graphing Trigonometric Functions1h 19m
5. Inverse Trigonometric Functions and Basic Trigonometric Equations1h 41m
6. Trigonometric Identities and More Equations2h 34m
7. Non-Right Triangles1h 38m
8. Vectors2h 25m
9. Polar Equations2h 5m
10. Parametric Equations1h 6m
11. Graphing Complex Numbers1h 7m

6. Trigonometric Identities and More Equations

Sum and Difference Identities

Trigonometry6. Trigonometric Identities and More EquationsSum and Difference Identities

Multiple Choice

Find $\cos\left(a+b\right)$ given $\cos a=\frac12$ , $\sin b=\frac12$ , & $a$ is in Q IV and $b$ is in Q II.

$\frac{\sqrt3}{4}$

$-\frac{\sqrt3}{2}$

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Find $\cos\left(a+b\right)$ given $\cos a=\frac12$ , $\sin b=\frac12$ , & $a$ is in Q IV and $b$ is in Q II.

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Find ﻿cos⁡(a+b)\cos\left(a+b\right)cos(a+b)﻿ given ﻿cos⁡a=12\cos a=\frac12cosa=21​﻿, ﻿sin⁡b=12\sin b=\frac12sinb=21​﻿, & ﻿aaa﻿ is in Q IV and ﻿bbb﻿ is in Q II.

Find $\cos\left(a+b\right)$ given $\cos a=\frac12$ , $\sin b=\frac12$ , & $a$ is in Q IV and $b$ is in Q II.