jika tanX =2/3(x lancip) hitunglah cos2a dan sin 2a

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jawab

tan A  = 2/3  = y/x
r² = 2²+3²= 13
r = √13
sin A  = y/r = 2/√13
cos A = x/r = 3/√13

cos 2A = 2 cos² A -1
= 2 (9/13) - 1
= 18/13 -1
= 5/13

sin 2A = 2 sin A cos A
= 2 (2/ √13)(3/ √13)
= 12/13