sin(π+a)sin(π-a)cosec^2a
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The answer is -1
sin(pi+a)=-sin(a) [since pi+a is in 3rd quadrant and in 3rd quadrant sine is negative]
sin(pi-a)=sin(a) [since pi-a is in 2nd quadrant and sine is positive in 2nd quadrant]
therefore,sin(pi-a)×sin(pi+a)=-sin^2a
and -sin^2a×cosec^2a=-1
sin(pi+a)=-sin(a) [since pi+a is in 3rd quadrant and in 3rd quadrant sine is negative]
sin(pi-a)=sin(a) [since pi-a is in 2nd quadrant and sine is positive in 2nd quadrant]
therefore,sin(pi-a)×sin(pi+a)=-sin^2a
and -sin^2a×cosec^2a=-1
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