Question

sin pie/10 - sin 13pie/10 = ?
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Answer 1

Step-by-step explanation:

= sin(π/10) sin(3π/10)

= sin(18°) sin (π + (3π/10))

= sin (18°) (- sin(3π/10))

= - sin(18°) sin (54°)

= - sin(18°) sin(90°-54°)

= - sin (18°) cos (36°)

sin 18 = (√5 - 1) /4

cos 36 = (√5 + 1) /4

= - (√5 - 1)/4 × (√5 + 1)/4

= - ((√5)^2 - 1^2) /16

= - (5-1)/16

= - 4/16

= - 1/16

Hope this helps.

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