Use the angle sum or difference identity to find the exact value of each?
cos 15 degrees
A)- (squareroot6)-(squareroot2)/4
B)(squareroot6)+(squareroot2)/4
C)(squareroot6)-(squareroot2)/4
D)(squareroot2)-(squareroot6)/4

Question

Use the angle sum or difference identity to find the exact value of each?
cos 15 degrees
A)- (squareroot6)-(squareroot2)/4
B)(squareroot6)+(squareroot2)/4
C)(squareroot6)-(squareroot2)/4
D)(squareroot2)-(squareroot6)/4

jazzyfa30 · Answer

@ganeshie8

ganeshie8 · Answer

hint : 15 = 45-30

ganeshie8 · Answer

cos(15) = cos(45 - 30)

jazzyfa30 · Answer

So i have to use my unit circle

ganeshie8 · Answer

apply cos(A - B) formula

ganeshie8 · Answer

yes u need to memorize sin/cos values for 45 and 30 degrees

jazzyfa30 · Answer

cos45 = $$\sqrt{2}/2$$ cos 30=$$\sqrt{3}/2$$
sin45=$$\sqrt{2}/2$$ sin 30= 1/2

ganeshie8 · Answer

excellent ! plug them in and simplify

jazzyfa30 · Answer

isnt it subtraction

jazzyfa30 · Answer

I got c

ganeshie8 · Answer

sorry i gave u the wrong formula :/

ganeshie8 · Answer

correct formula :

cos(45 - 30) = cos45 cos30 $\color{red}{+}$ sin45 sin30

ganeshie8 · Answer

please work it again lol, really sorry

jazzyfa30 · Answer

ok so its the same just different symbol

ganeshie8 · Answer

yup !

jazzyfa30 · Answer

can you help me with one more like that

ganeshie8 · Answer

sure :)