Question

Use an addition or subtraction formula to find the exact value.
cos (-pi/12)

Answer 1

cos (-pi/2) = cos (pi/2) = 0

Answer 2

Or, using addition/subtraction formula,

cos ( 0 - pi/2) = cos 0 cos pi/2 + sin 0 sin pi/2
= 1(0) + 0(1)
= 0

Answer 3

0- pi/2 doesn't give you -pi/12. @Easyaspi314

Answer 4

Sorry, I read the question wrong, I thought it said -pi/2

Answer 5

- pi/12 = -15 degrees

Answer 6

how did you get that?

Answer 7

Use the formula for cos(30-45) = cos - 15 degrees

Answer 8

pi radians = 180 degrees, so - pi/12 radians = -180/12 = -15 degrees

Answer 9

In your text there is a formula for cos (x - y), the difference formula for cos

Answer 10

So cos (30 - 45) according to the formula =
cos 30 cos 45 + sin 30 sin 45

Answer 11

You're suppoised to know that cos 30 = sqrt(3)/2; cos 45 = sqrt(2)/2; sin 30 = 1/2; sin (45) = sqrt (2)/2
so cos (30-45) = what? plug in