3(sinх)^2+cos2х=3 (sinх)^2 +(cosх)^2- (sinх)^2=(sinх)^2+(sinх)^2+(cosх)^2=(sinх)^2+1

(sinх)^2=1/(1+(ctgx)^2)

(ctgx)^2=1/(tgx)^2=1/9

(sinх)^2=1/(1+1/9)=0.9

3(sinх)^2+cos2х=1.9