<span>-х^2+21х=0
х^2-21х=0
х(х-21)=0
х1=0 или х-21=0 х2=21
</span>
<span>2x+6+x^2+3x
x^2+5x+6=0</span>
D=b^2-4ac
D=25-4*1*6
D=1
x=-b(+-)D/2a
x1=(-5+1)/2=-2
x2=(-5-1)/2=-3
x(x+2)(x+3)
Tg1° * tg3° * tg5° * ... * tg85° * tg87° * tg89° = (tg1° * tg89°) * (tg3° * tg87°) *
* (tg5° * tg85°) * ... tg45° = (tg1° * Ctg1°) * (tg3° * Ctg3°) * (tg5° * Ctg5°) *
* ... * tg45° = 1 * 1 * 1 * .... * 1 = 1
Y=kx+(-5)
10=k*(-2)-5
-2k=15
k=-7,5