Question

Cho x-y=7. Tính

A= x.(x+2) + y . ( y-2) - 2xy + 37

Answer 1

Ta có A=x(x+2)+y(y-2)-2xy+37

= x^2 +2x + y^2 - 2y - 2xy +37

=(x^2 +y^2 -2xy +1 +2x - 2y) +36

=(x -y +1)^2 +36

= (7+1)^2 +36 = 64 +36 =100

Answer 2

A=x(x+2)+y(y-2)-2xy+37

   =x²+2x+y²-2y-2xy+37

   =(x²-2xy+y²)+(2x-2y)+37

   =(x-y)²+2(x-y)+37

   =7²+2.7+37

   =49+14+37

   =100