buktikan sin(a-b)sin(a-b)=sin^2a-sin^2b
Matematika
parkminrin68
Pertanyaan
buktikan sin(a-b)sin(a-b)=sin^2a-sin^2b
1 Jawaban
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1. Jawaban Anonyme
TRIgonomeTRI
sin (a + b) . sin (a - b)
= -1/2 (cos (a + b + a - b) - cos (a + b - a + b))
= -1/2 (cos 2a - cos 2b)
= -1/2 (1 - 2 sin² a - (1 - 2 sin² b))
= -1/2 (-2 sin² a + 2 sin² b)
= sin² a - sin² b
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