Question

Solve the equation cos x° = sin 40°, where 0 < x < 90.

Answer 1

For 0 < x < 90,
cos (90-x) = sin (x), and
sin (90-x) = cos(x)

Answer 2

I still dont know how to get the answer lol

Answer 3

Ehm.... Pick one identity from above first.

Answer 4

cos (90-x) = sin (x), is that what you mean?

Answer 5

You can pick either one lol
So, your choice is cos(90-x) = sin(x). Let's just rename x as "a". So, we have
cos(90-a) = sin(a)
Compare this with what you have now: sin 40
What is a in this case?

Answer 6

40? I dont know I'm terrible at geometry

Answer 7

40 is right, and it's not geometry, haha!
Now, substitute a by 40, you have cos(90-50) = sin(40). Can you simplify the left side?

Answer 8

Oh well this a question on my geometry test lol. 90-50 is 40

Answer 9

Aiya! My bad! It should be cos(90-40) = sin(40). Can you simplify the left side again?

Answer 10

90-40=50

Answer 11

Yup! So, you have cos(50) = sin(40). I guess that's all?!

Answer 12

Yes, thanks a lot!

Answer 13

You're welcome~