Question

решите уравнение cos x+ cos 7x=2

Answer 1

cos(7x) + cos(x) = 2 * cos((7x+x)/2) * cos((7x-x)/2) = 2 * cos(4x) * cos(3x)
cos(4x) * cos(3x) = 1
cos(0) = 1
x=0
1 + 1 = 2
1 * 1 = 1