Question

Найти sina, cosa, tga если дано :
ctga=-8/15 , п/2 < a <п

Answer 1

1) ctgx * tgx = 1
ctgx = -8/15
tgx = -15/8;
2) 1 + $tg^{2}x$ = 1/$cos^{2}x$;
1 + 225/64 = 1/$cos^{2}x$;
289/64 = 1/$cos^{2}x$;
17/8 = 1/ cosx;
17cosx = 8;
cosx = 8/17;
3) $cos^{2}x$ + $sin^{2}x$ =1;
64/289 + $sin^{2}x$ = 1;
$sin^{2} x$ = 1 - 64/289;
$sin^{2} x$ = 225/289;
sinx = 15/17

sinx = 15/17
tgx = -15/8;
8/17;