Tg a * ctg a = 1; ⇒
(tg a + ctg a)^2 = tg^2 a + 2 tga * ctg a + ct^2 a = tg^2 a + ctg^2 a + 2*1;
A = tg^2 a + ctg^2 a + 2;
tg^2 a + ctg^2 a = A - 2
1) x-16<span><0
x</span><span><16
2) 28x+4</span><span>>0
28x</span><span>>-4
x</span><span>>-1/7
3) 31x+63</span><span>>36x+23
31x-36x</span><span>>23-63
-5x</span><span>>-40
x</span><span>>8</span>
Х^6+6у^4х^3+9у^8 по формуле (а+б)^2
Вот. Скачай программу "Photomath"