Question

Bài 2: cho B= xy³-x²y. tính giá trị của B khi :  a, x=1,y=1;    b, x=-1,y=-1;    c,x=1, y=-1;      d, x=-1; y=1.

Answer 1

a: \(B=xy\left(y^2-x\right)=1\cdot1\cdot\left(1^2-1\right)=0\)

b: \(B=xy\left(y^2-x\right)=-1\cdot\left(-1\right)\cdot\left[\left(-1\right)^2-\left(-1\right)\right]=1\cdot\left(1+1\right)=2\)

c: \(B=xy\left(y^2-x\right)=1\cdot\left(-1\right)\cdot\left[\left(-1\right)^2-1\right]=0\)

d: \(B=xy\left(y^2-x\right)=-1\cdot1\cdot\left[1^2-\left(-1\right)^2\right]=0\)

Answer 2

Bài 2:

\(B=xy^3-x^2y=xy\left(y^2-x\right)\)

a) \(x=1;y=1\Rightarrow B=1.1.\left(1^2-1\right)=0\)

b) \(x=-1;y=-1\Rightarrow B=\left(-1\right).\left(-1\right).\left[\left(-1\right)^2-\left(-1\right)\right]=2\)

c) \(x=1;y=-1\Rightarrow B=1.\left(-1\right).\left[\left(-1\right)^2-\left(-1\right)\right]=-2\)

d) \(x=-1;y=1\Rightarrow B=\left(-1\right).1.\left[1^2-\left(-1\right)\right]=-2\)