sin a + b is equal to sin a into cos b + cos b into sin
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**************************************************
sin( A + B ) = sinAcosB + cosAsinB
**************************************************
1) Here , we assume
A = 45° , B = 30°
cos 15°
= cos ( 90 - 75 )
= sin 75°
= sin ( 45 + 30 )
= sin45cos30 + cos45sin30
= ( 1√2 )( √3/2 ) + ( 1/√2 )( 1/2 )
= ( √3/2√2 ) + 1/2√2
= ( √3 + 1 ) / 2√2
Therefore,
cos15° = sin75° = = ( √3 + 1 ) / 2√2
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