Question

Trigonometry help, please? I'm not understanding how to solve this.

Answer 1

Use the identity

cos(A+B) = cos(A)cos(B) - sin(A)sin(B)

Answer 2

What do I substitue A and B for? Becuase I was taught to substitute it with known degrees on a Unit Circle

Answer 3

But I'm not sure if that's what I should do here

Answer 4

Draw out the triangle for angle A

Answer 5

What is that missing side?

Answer 6

Opposite over hypotenuse right?

Answer 7

that's sin(A), yes

Answer 8

Alrighty, hold on

Answer 9

but we want to find cos(A), so we need to find that missing side first

Answer 10

okay, and since I don't know A, would I use the inverse so I know the measure of the angle?

Answer 11

Or well, so I can find it

Answer 12

did you find the length of that missing side?

Answer 13

no need to find the angle A itself

Answer 14

Okay, sorry Lol give me a sec

Answer 15

alright

Answer 16

Okay, I got 17.7 or 18 as the missing length

Answer 17

how did you get that?

Answer 18

Woah, I solved for hypostenuse :p

Answer 19

ah gotcha

Answer 20

okay, 5 as the missing legnth Lol.

Answer 21

you got it, so let's update the triangle