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Evaluate: cos70∘sin20∘+cos59∘sin31∘-8sin230∘

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Question

Evaluate:

`cos70^circ/(sin20^circ) + cos59^circ/(sin31^circ) - 8 sin^2 30^circ`

Evaluate
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Solution

`cos70^circ/(sin20^circ) + cos59^circ/(sin31^circ) - 8 sin^2 30^circ`

= `cos(90^circ - 20^circ)/(sin20^circ) + cos(90^circ - 31^circ)/(sin31^circ) - 8(1/2)^2`

= `sin20^circ/(sin20^circ) + sin31^circ/(sin31^circ) - 2`

= 1 + 1 – 2

= 0

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