\(A=x^3-y^3-x^2+2xy-y^2\)
\(A=\left(x-y\right)\left(x^2+xy+y^2\right)-\left(x^2-2xy+y^2\right)\)
\(A=\left(x-y\right)\left[\left(x-y\right)^2+3xy\right]-\left(x-y\right)^2\)
\(A=-5.\left[\left(-5\right)^2+3.\left(-6\right)\right]-\left(-5\right)^2\)
\(A=-5.7-25\)
\(A=-60\)
\(A=x^3-y^3=\left(x-y\right)^3+3xy\left(x-y\right)\)
\(=\left(-5\right)^3+3\cdot\left(-6\right)\cdot\left(-5\right)\)
\(=-125+90=-35\)
\(\left(x+y\right)^2=\left(x-y\right)^2+4xy=25-24=1\)
=>x+y=1 hoặc x+y=-1
\(B=x^2+2xy-y^2\)
\(=\left(x-y\right)\left(x+y\right)+2xy\)
\(=-5\left(x+y\right)-12\)
Khi x+y=1 thì B=-17
Khi x+y=-1 thì B=-7
