Buktikan jika 2 sin ( 7 π / 4 a) sin ( π/4 a) = -cos 2 a
Matematika
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Pertanyaan
Buktikan jika 2 sin ( 7 π / 4 a) sin ( π/4 a) = -cos 2 a
1 Jawaban
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1. Jawaban Anonyme
jawb
2 sin (7π/4 + a) sin (π/4 + a) =
= - ( - 2 sin (7π/ 4 + a ) sin (π/4 + a)
= - {cos (7π/4 + a + π/4 + a ) - cos (7π/4 + a - π/4 - a ) }
= - {cos (2π + 2a) - cos (3π/2 )
= - { cos 2a - 0)
= - cos 2a