Срочно решите уравнение cos3x cos6x=cos4x cos7x

Question

Срочно решите уравнение cos3x cos6x=cos4x cos7x

Answer 1

(cos(7х-4х)) /2+(cos(7х+4х)) /2=(cos(6х-3х)) /2+(cos(6х+3х)) /2
(cos3х) /2+(cos11х) /2=(cos3х) /2+(cos9х) /2
cos11х=cos9х
11х=+-9х
х=0 ---> x=2пи+-2пи*n