Question #f5163

1 Answer
P dilip_k
Dec 20, 2016

LHS=sin( pi/5)sin ((2pi)/5)sin(pi-(2pi)/5)sin(pi-pi/5)

=sin( pi/5)sin ((2pi)/5)sin((2pi)/5)sin(pi/5)

=sin^2( pi/5)sin^2((2pi)/5)

=(sin( pi/5)sin((2pi)/5))^2

=((sqrt(10-2sqrt5)/4)(sqrt(10+2sqrt5)/4))^2

=(100-20)/256=80/256=5/16

Proved

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