Math, asked by sahil908, 1 year ago

sin square 42 - cos square 78

Answers

Answered by Smartyyogi45
8

 ( { \sin }^{2} 42 \:  -  { \cos}^{2} 78)
 { \sin }^{2}42 \:  +  \:  { \sin}^{2} 78 \:  - 1
 { \sin }^{2} 120 \:  - 1
 (\sin(120)  - 1)( \sin(120)   + 1)
Answered by book113322
5
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.
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