Question

sin square 42 - cos square 78

Answer 1

$( { \sin }^{2} 42 \: - { \cos}^{2} 78)$
${ \sin }^{2}42 \: + \: { \sin}^{2} 78 \: - 1$
${ \sin }^{2} 120 \: - 1$
$(\sin(120) - 1)( \sin(120) + 1)$

Answer 2

here your answer plz.
cos square 42-sin square 78
we have cos square A-sin square B=cos(A+B)cos(A-B)
using this we get.
LHS =-(cos 120cos36)
=cos 36/2
=(5 1/2+1)/8=Rhs.
I hope it is helpfull for you.
plz mark as brainliest.