Question

Plz solve only 19. 20 number question plz someone solve it

Answer 1

sorry  i do not know
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Answer 2

Hey there !!!!

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sin²5°+sin²10°+sin²15°..........+sin²45°...........+sin²80+sin²85°+sin²90°

sin²Ф=cos²(90-Ф)

So,

sin²5+sin²10.........+sin²45............+cos²10+cos²5+sin²90°

Rearranging terms with same angles

=sin²5+cos²5+sin²10+cos²10..............sin²45+sin²90-----Equation 1

We know that sin²Ф+cos²Ф=1

So in equation 1 starting from 5° to 40°there exists 8 pairs which are of the form  sin²Ф+cos²Ф=1

So equation 1 changes to 

= 8+sin²45+sin²90

=8+1/2+1

=9+1/2=19/2

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cosα=1/2                         tanβ=1/√3

cosα=cos60                    tanβ=tan30

α=60                               β=30

sin(α+β)=sin(60+30)=sin90=1

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Hope this helped you................