Question

Us the Sum Formula to:
a. Find the exact value of cos 105 degrees

b. Find the exact value of sin 5pi/12

Answer 1

Hint for part a :

105 = 60 + 45

Answer 2

@jim_thompson5910

Answer 3

cos(A+B)=?

Answer 4

@rvc wait is that it?

Answer 5

the question already provides a hint
use the sum formula
and we know to use the sum formula for cosine
since we are asked to find cos(105)
and @ganeshie8 gave you the hint that 105 is 60+45
and @rvc is just trying to get you to look at your identitys sheet and copy over the identity mentioned for cos(A+B)
and replace the A with 60 and the B with 45
and evaluate using unit circle

Answer 6

how did he get 60 and 45 though? @freckles

Answer 7

60 and 45 when added gives you 105

Answer 8

yeah but why those in particular? 100 + 5 gives you 105 too?

Answer 9

is 100 and 5 on the unit circle?

Answer 10

60 and 45 are

Answer 11

well we have those values already and can easily plug in