Question

Tga\tga+ctga=sin²a доказать тождество

Answer 1

$\frac{tgx}{tgx + ctgx} = sin^2x \\ \frac{tgx}{ \frac{1}{ctgx} + ctgx} = sin^2x \\ \frac{tgx}{ \frac{1 + ctg^2x}{ctgx} } = sin^2x \\ \frac{tgx}{ \frac{1 + ctg^2x}{ctgx} } = sin^2x \\ \frac{tgx}{1 + ctg^2x} : ctgx = sin^2x \\ \frac{tgx}{1 + ctg^2x} * \frac{1}{ctgx} = sinx^2 \\ \frac{1}{1 + ctg^2x} = sin^2x \\ \frac{1}{ \frac{1}{sin^2x} } = sin^2x \\ sin^2x = sin^2x$