Lesben 1)a²-2.a.b +b²=(a-b)²
  a²-b²=(a+b)(a-b)
 (3,17²-2.3,17.1,17+1,17²)/(6,75²-3,25²)=(3,17-1,17)²/(6,75+3,25)(6,75-3,25)=
=2²/10.3,5=4/35

2)(a-1)(a+3)-(a+1)²=a²+3a-a-3-a²-2a-1=-4
3)(x-2y)/(x-3y) .(x/(3x-6y) +y/(2y-x))=
=(x-2y)/(x-3y) .( x/3(x-2y) -y/(x-2y))=
=(x-2y)/(x-3y) . (x-3y)/(3(x-2y)=
=1/3
4)(8x-3)(2x+1)=(4x-1)²
16x²+2x-3=16x²-8x+1
2x-3=-8x+1
10x=4
x=4/10, x=2/5 , x=0,4