RT,求值cosπ/11*cos2π/11*cos3π/11*cos4π/11*cos5π/11
1个回答

原式

=(cosπ/11*cos2π/11*cos3π/11*cos4π/11*cos5π/11*2sinπ/11)/2sinπ/11

=(sin2π/11*cos2π/11*cos3π/11*cos4π/11*cos5π/11)/2sinπ/11

=(1/2*sin4π/11*cos3π/11*cos4π/11*cos5π/11)/2sinπ/11

=(1/4*sin8π/11*cos3π/11*cos5π/11)/2sinπ/11

=(1/4*sin3π/11*cos3π/11*cos5π/11)/2sinπ/11

=(1/8*sin6π/11*cos5π/11)/2sinπ/11

=(1/8*sin5π/11*cos5π/11)/2sinπ/11

=(1/16*sin10π/11)/2sinπ/11

=1/32