Tolong beserta caranya ya, kalau bisa caranya di foto biar enak di catat

cos ( A - B ) = cos A . cos B + sin A . sin B
cos ( A - B ) = 1/2 cos ( A - B ) + 1/2 cos ( A + B ) + 1/4
cos ( A - B ) - 1/2 cos ( A - B ) = 1/2 cos ( π / 3 ) + 1/4
1/2 cos ( A - B ) = ( 1/2 ) ( 1/2 ) + 1/4
cos ( A - B ) = 2 ( 1/4 + 1/4 )
cos ( A + B ) = 1 ( A )



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