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
