Question

已知A=3a²b-ab²,b=ab²-3a²b 求5A-B. 若|a+1/2|+(b-1/3)²=0，求5A-B的值

你们的答案都不一样 - -

Answer 1

5A-B=18a2-6ab2.由题中所给的等式的|a+1/2|大于等于0,(b-1/3)2大于等于0，可以得出a=-1/2,b=1/3,所以5A-B=3.25

Answer 2

∵|a+1/2|+(b-1/3)²=0，|a+1/2|≥0， (b-1/3)²≥0
∴|a+1/2|=0，(b-1/3)²=0
∴a=-1/2,b=1/3

5A-B = 15a²b-5ab²-(ab²-3a²b)= 18a²b-6ab² = 18*(-1/2)^2*(1/3)-6(-1/2)*(1/3)^2=11/6

Answer 3

|a+1/2|+(b-1/3)²=0
a+1/2=0, b-1/3=0
a=-1/2
b=1/3
5A-B=(3a²b-ab²)-(ab²-3a²b)
=6a²b-2ab²
=2ab(3a-b)
=2*(-1/2)*1/3[3(-1/2)-1/3]
=11/18

Answer 4

5A-B=18a²b-6ab²
|a+1/2|+(b-1/3)²=0
a=-1/2.b=1/3
5A-B=18a²b-6ab²=18*(-1/2)^2*(1/3)-6*(-1/2)*(1/3)=3/2+1=5/2