Question

Trig Identities....Half Angles help PLEASEEEEE!!!

Can someone explain what the teacher wrote on the board for me please???


Cos2A = cos^2A-sin^2A
= 1 - 2sin^2 A (What happened here???????)

Answer 1

sin^2 + cos^2 =1

Answer 2

1-cos^2==sin^2

Answer 3

sub in ...
Cos2A=cos^2A-1+cos^2A

Answer 4

Cos2A=2cos^2A -1

Answer 5

now do same thing with 1-sin^2= cos^2


and you should get the identity you teacher wrote


sooooo

1-sin^2=cos^2


sub into
Cos2A = cos^2A-sin^2A

Cos2A=1-sin^2A-sin^A


==1-2sin^2A

Answer 6

HMmm let me process what you said

Answer 7

Thank you! I finally get it!

Answer 8

yw