Question

Trig help, please. Medal and fan if you help me out.

1. Evaluate cos(a+b)
sin a = -7/25, cot b = -8/15
neither are in quadrant IV


2. Evaluate cos(a-b)
tan a = 4/3, sin b = -7/25;
pi < a < 3pi/2,
3pi/2 < b < 2pi

(Exact answers no decimals)

Answer 1

Here are some hints
1.)If you are giving 1 trigonometric ratio, you can find all the others using identities
2.)Try using the formula cos(a+b)=cosacosb-sinasinb
3.)The pythagorean triplets in questions are
7,24,25 and 8,15,17 and 3,4,5

Answer 2

\(\huge\color{red}{cos(a+b)=cosacosb-sinasinb}\)

\(\huge\color{red}{cos(a-b)=cosacosb+sinasinb}\)

Answer 3

Thank you guys so much this really helped

Answer 4

:)