1
x²+13x+42=(x+6)(x+7)
x1+x2=-13 U x1*x2=42⇒x1=-7 U x2=-6
3x²-11x+6=3(x-2/3)(x-3)=(3x-2)(x-3)
D=121-72=49
x1=(11-7)/6=2/3 U x2=(11+7)/6=3
2
(x²-10x+21)/(2x²-15x+7)=(x-7)(x-3)/(2x-1)((x-7)=(x-3)/(2x-1)
x²-10x+21=(x-7)(x-3)
x1+x2=10 U x1*x2=21
x1=7 U x2=3
2x²-15x+7=2(x-1/2)(x-7)=(2x-1)(x-7)
D=225-56=169
x1=(15-13)/4=1/2 U x2=(15+13)/4=7
3
1)(y+5)/(y-2)(y-5) -(y-2)/(y-5)(y+2)=(y²+7y+10-y²+4y-4)/(y-5)(y²-4)=
=(11y+6)/(y-5)(y²-4)
2)(11y+6)/(y-5)(y²-4) :(11y+6)/(y²-4)=(11y+6)/(y-5)(y²-4) *(y²-4)/(11y+6)=
=1/(y-5)