Question

докажите тождества:ctga-tga=2ctg2a

Answer 1

$frac{cosa}{sina} - frac{sina}{cosa} = frac{cos^{2}a-sin^{2}a}{sina*cosa} = frac{cos2a}{ frac{1}{2}sin2a } = frac{2cos2a}{sin2a}=2ctg2a$
2ctg2a

Answer 2

. . . . . . . . . . . . . . . . .