ПрофиЗнания 3) sin^2a/cos^2a * cos^2a + cos^2a/sin^2a  * sin^2a = sin^2a+cos^2a=1

2)ctga=8/15

tga*ctga=1
tga=1*15/8

1+tg^2a= 1/ cos^2a
1+225/64 = 1/cos^2a
289/64=1/cos^2a
cos^2a=64/289
cosa=8/17

sina=√1-64/289 = √225/289=15/17

1)sin^2a/cos^2a - sin^2a = sin^2a * sin^2a/cos^2a
sin^2a-sin^2acos^2a / cos^2a = sin^4a/cos^2a
sin^2a(1-cos^2a)/cos^2a= sin^4a/cos^2a
 sin^2a*sin^2a/cos^2a =  sin^4a/cos^2a
sin^4a/cos^2a= sin^4a/cos^2a