Question

a, x(x-y)+y(x+y) tại x=-6 và y=8

b, x(x^2-y) -x^2(x+y)+y(x^2-x) tại x=1/2 và y=-100

Answer 1

\(a,x\left(x-y\right)+y\left(x+y\right)\\ =x^2-xy+xy+y^2\\ =x^2+y^2\\\)

Thay \(x=-6;y=8\)

\(\left(-6\right)^2+8^2=100\)

\(-------------\\ b,x\left(x^2-y\right)-x^2\left(x+y\right)+y\left(x^2-x\right)\\ =x^3-xy-x^3-x^2y+x^2y-xy\\ =-2xy\\ \)

Thay \(x=\dfrac{1}{2};y=-100\)

\(-2.\dfrac{1}{2}.\left(-100\right)=100\)

Answer 2

a)

\(x\left(x-y\right)+y\left(x+y\right)=x^2-xy+xy+y^2=x^2+y^2\)

\(thay\) \(x=-6,y=8\) co \(\left(-6\right)^2+8^2=36+64=100\)

b)

\(x\left(x^2-y\right)-x^2\left(x+y\right)+y\left(x^2-x\right)=x^3-xy-x^3-x^2y+x^2y-xy=-2xy\)thay \(x=\dfrac{1}{2},y=-100\) ta co

\(-2\cdot\dfrac{1}{2}\cdot\left(-100\right)=100\)