Question

доказать тождество sin 72-sin18:cos72-cos18=-1

Answer 1

$\frac{sin72-sin18}{cos72-cos18}= \frac{sin72-sin(90-72)}{cos72-cos(90-72)}$$= \frac{sin72-cos72}{cos72-sin72}=- \frac{cos72-sin72}{cos72-sin72}=-1$
-1=-1
Доказано.