Question

ПОМОГИТЕ,ПОЖАЛУЙСТА!!!

Answer 1

Сумма корней

$\frac{ \pi }{11} + \frac{2 \pi }{11}+ \frac{3 \pi }{11}+ \frac{ 4\pi }{11}+ \frac{5 \pi }{11}+ \frac{\pi}{2} = \boxed{\frac{41\pi}{22}}$

Answer 2

cos4xcos5x-cos6xcos7x=0
1/2cosx+1/2cos9x-1/2cosx-1/2cos13x)=0
1/2cox9x-1/2cos13x=0
cos9x-cos13x=0
-2sin(-2x)sin11x=0
sin2x=0⇒2x=πn⇒x=πn/2
0≤πn/2≤π/2
0≤n≤1
n=0  x=0
n=1  x=π/2
sin11x=0⇒11x=πn⇒x=πn/11
0≤πn/11≤π/2
0≤n≤5 1/2
n=0  x=0
n=1  x=π/11
n=2  x=2π/11
n=3  x=3π/11
n=4  x=4π/11
n=5  x=5π/11
0+π/2+0+π/11+2π/11+3π/11+4π/11+5π/11=π/2+15π/11=41π/22