a) (x-3)/6=(2x+1)/3 -3
(x-3)/6=(2x+1-9)/3
3(x-3)=6(2x-8)
3x-9=12x-48
9x=39
x=39/9
x=13/3
b) { x-4x-4y=2
2x-2y-4y=16
{-3x-4y=2 /×2
2x-6y=16 /×3
{-6x-8y=4
6x-18y=48
------------------(+)
-26y=52
y=-2
{2x-6y=16
{2x+12=16
{2x=4
{x=2
c)x(x+2)+2(x-2)-1=0
x²+2x+2x-4-1=0
x²+4x-5=0
delta=16+20
delta=36
x1=(-4-6)/2. x2=(-4+6)/2
x1=-5. x2=1
d)2/7a=4/21
42=28a
a=42/28
a=6/4
a=3/2
