2sin14x×cos7x+sin7x=0

Question

2sin14x×cos7x+sin7x=0

Answer 1

2sin14xcos7x+sin7x=0;
4sin7xcos²7x+sin7x=0;
sin7x(4cos²7x+1)=0;
sin7x=0;⇒7x=nπ;n∈Z;⇒x=nπ/7;n∈Z;
cos²7x=-1/4⇒cos²7x>0⇒нет решения.

Comments

cos^2 (7x)<0-->нет решения