po formule sin(a+b)=sinacosb+cosasinb

 sin(6x+x)=1/2

sin7x=1/2

7x=(-1)^k p/6+pk

x=(-1)^k p/42+pk/7

 cos(a+b)=cosacosb-sinasinb

cos(5x+7x)=koren`3/2

cos12x=koren`3/2

12x=p/6+2pk

x=p/72+pk/6