2) {x+y=23 inmultim -3
{3x+7y=113
{-3x-3y=-69
{3x+7y=113
3x-3x+7y-3y=113-69
4y=44
y=44/4
y=11
din x+y=23 rezulta x+11=23
x=23-11
x=12
3)a) (2•x+3)•(2•x+4)=56
4x²+8x+6x+12=56
4x²+14x-56+12=0
4x²+14x-44=0 :2
2x²+7x-22=0
Δ=49+4·2·22=49+176=225
x1=(-7+15)/4=8/4=2
x2=(-7-15)/4=-22/4=-11/2=-5,5
S={-5,5; 2}
4) nr.consecutive sunt: a, a+1, a+2
(a+a+1+a+2):7=13 rest 5
(3a+3)=13x7+5
3(a+1)=96
a+1=96:3
a+1=32
a=32-1
a=31
deci nr.sunt: 31,32,33
5)