Formule de calcul prescurtat:
(A+B)^2=A^2+2AB+B^2
(A-B)^2=A^2-2AB+B^2
(A+B)(A-B)=A^2-B^2
4x/(x+3)-x/(x-3)=12/(9-x)^2
4x/(x+3)-x/(x-3)=12/(3-x)(3+x)
4x/(x+3)-x/(x-3)=-12/(x-3)(x+3)
Numitorul comun e (x-3)(x+3).
4x(x-3)-x(x+3)=-12
4x^2-12x-x^2-3x=-12
3x^2-15x=-12
3x(x-5)=-12
x(x-5)=-4
x^2-5x+4=0
x^2-x-4x+4=0
x(x-1)-4(x-1)=0
(x-1)(x-4)=0
x-1=0=>x1=1
x-4=0=>x2=4
S={1, 4}
9-x^2=3^2-x^2=(3-x)(3+x)
