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Q.

Statement (A): sin25°+sin210°+........... +sin290°=9.5

            Statement (B): If secθ+tanθ=1p , then  secθtanθ=p

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a

Both A and B are true

b

Both A and B are false

c

A is true and B is false

d

A is false and B is true

answer is A.

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Detailed Solution

A:sin25°+sin210°+.....+sin285°+sin290°=(sin25°+sin285°)+(sin210°+sin280°)+(sin215°+sin275°)+(sin220°+sin270°)+(sin225°+sin265°)+(sin230°+sin260°)+(sin235°+sin255°)+(sin240°+sin250°)+(sin245°+sin290°)

But we know that  sin(90°θ)=cosθ

sin85°=sin(90°5°)=cos5°

Similarly sin80°=cos10°

sin75°=cos15°......

=(sin25°+cos25°)+(sin210°+cos210°)+(sin215°+cos215°)+(sin220°+cos220°)+(sin225°+cos225°)+(sin230°+cos230°)+(sin235°+cos235°)+(sin240°+cos240°)+(sin245°+sin290°)=1+1+1+1+1+1+1+1+(12)2+(1)2=9+12=9+0.5=9.5

Statement B sec2θ+tan2θ=1

(secθ+tanθ)(secθtanθ)=1

1p(secθtanθ)=1

secθtanθ=p

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