log3(12+5cos(2a)), если tg a = 2
одз a ∈ R
cos(2a) = (1 - tg^2(a)/(1 + tg^2(a))
log(3) ( 12 + 5*(1 - 2²)/(1 + 2²)) = log(3) ( 12 - 5*3/5) = log(3) ( 12 - 3) = log(3) 9 = log(3) 3² = 2
