Question #cb7c5

1 Answer
Jul 4, 2016

=132

Explanation:

cos(π11)cos(2π11)cos(3π11)cos(4π11)cos(5π11)

=4sin(π11)cos(π11)cos(2π11)cos(3π11)cos(4π11)cos(5π11)4sin(π11)

=2sin(4π11)cos(4π11)cos(π8pi11)cos(5π11)8sin(π11)

=2sin(8π11)cos(8π11)cos(5π11)16sin(π11)

=2sin(16π11)cos(5π11)32sin(π11)

=2sin(π+5pi11)cos(5π11)32sin(ππ11)

=sin(10π11)32sin(10π11)

=132

Explanation of steps

Multiplyig both numerator and denominator by 4sin(π11)

Applying identity 2sinAcosA=sin2A