how do you solve 1 - cos^2 (20) - cos^2 (70)

Question

how do you solve   1 - cos^2 (20) - cos^2 (70)

anonymous · Answer

hello

ash2326 · Answer

cos^2+sin^2x=1
Hi jay
cos x= sin (90-x)
cos ^2 x=1- sin^2x
cos 20= sin 70
so
1--sin^2 70-cos^2 70
1-(sin ^2 70+cos ^2 70)
1-1
0

anonymous · Answer

hm...

anonymous · Answer

why do youadd sin and cos ?

ash2326 · Answer

cos 20 is equal to sin 70 ,I substituted that in the equation.
we have cos^2x+sin^2x=1 , this is an identity
i used it
cos^2 70+sin2^ 70=1
so 1-1=0

anonymous · Answer

but originally if cos20 changes to sin 70 then the next sign - doesn't have to be same ?
instead of +?

ash2326 · Answer

see we have 
1-(cos^2 20)-cos^2 70
cos 20 = sin 20
cos^2 20= sin^2 70
1-(sin^2 70)-cos^2 70
1-1

ash2326 · Answer

it's - only
i took - out of the bracket
-(sin2^ 70+cos^2 70)
1- (1)

anonymous · Answer

then doesn't -(sin2^ 70+cos^2 70)
1- (1) -> this change it to 1 - - ( 1) ?? sorry i am such a burden