<span>5x^2+20xy+20y^2 = 5*(x^2+4xy+4y^2) = 5*(х+2)^2 </span>
A) tg(180 - a) / ctg (90 - a) = -tg a / tg a = -1
б) (cos²(90 - α )-1) / cos (180 - α) = (sin<span>² α -1) / (-cos α) = </span>- cos² α / (-cos α) = cos a
в) sin (π-α) / tg (π+a) = <span>sin α / tg a = </span><span>sin α cos a / sin a</span> = cos a
<em>Это может быть и 7.1, и 7.2 , и 7.3 , и 7.4 , и 7.5 , и 7.6 , и 7.7 , и 7.8 , и 7.9 , и 7.11 , и 7.34 и т.д. до 7.99999999...</em><span><em /></span><span><em /></span>
<span>7 в степени 3-2x=49 в степени 2x</span>
-15-2х²=-11х
2х²-11х+15=0
D=121-120=1
x₁=(11+1)/4=3
x₂=(11-1)/4=2,5