1. <span>7x(x+1)=21-7x
7x^2+7x=21-7x
7x^2+14x-21=0
x^2+2x-3=0
D=4-4*1*(-3)=16; Корень из D = 4
x1=-2+4/2=1 ; x2= -2-4/2 = -3
2. </span><span>y(y-1)=y+15
y^2-y=y+15
y^2-2y-15=0
По теореме Виетта:
y1=-3 ; y2=5</span>
(log3(x-2)- 1)^2+(x-5)^2=0
9y²-(3+2y)² = (3y-(3+2y))(3y+(3+2y)) = (3y-3-2y)(3y+3+2y)= (y-3)(5y+3)