sin9 cos 9/sin 48 sin 12=?
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Answered by
18
sin9°.cos9°/sin48°.cos12°
=2sin9°.cos9°/2sin48°.cos12°
use , formula ,
2sinA.cosA = sin2A
and 2sinA.cosB = sin(A + B) + sin(A - B)
= sin18°/{ sin(48° + 12°) + sin(48°-12°)
= sin18°/{ sin60° + sin36° }
we know,
sin18° = 1/2(√5 -1)
sin36° = 1/4√(10 -2√2)
= 1/2(√5 -1)/{ √3/2 + 1/4√(10-2√2) }
=2sin9°.cos9°/2sin48°.cos12°
use , formula ,
2sinA.cosA = sin2A
and 2sinA.cosB = sin(A + B) + sin(A - B)
= sin18°/{ sin(48° + 12°) + sin(48°-12°)
= sin18°/{ sin60° + sin36° }
we know,
sin18° = 1/2(√5 -1)
sin36° = 1/4√(10 -2√2)
= 1/2(√5 -1)/{ √3/2 + 1/4√(10-2√2) }
Answered by
6
Answer:
hope you know these formulas ,
sin c + sin d =2 sin c+d/2 sin c-d/2
apply to get the Sol.n
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