4х^2-5х-16х+20-4х^2+9
-21х+29=-21*(-1/3)+29=36
А)c^2-4d^2=(с-2d)(c+2d)
б)-25a^2+10ab-b^2=-(25a²-10a+b²)=-(5a-b)²
<span>в)ax+by-ay-bx=(ax-ay)+(by-bx)=a(x-y)+b(y-x)=a(x-y)-b(x-y)=(a-b)(x-y)</span>
<span>X/2+y/3=3
x/3+y/2=1/3</span>
складываем оба
x/2+x/3+y/3+y/2=3 1/3
(5x+5y)/6=10/3
x+y=4
x=4-y
(4-y)/2+y/3=3
2-y/2+y/3=3
y/6=-1
y=-6
x=10