Question

初中数学先化简，再求值，(a/a的平方-b的平方-1/a+b)÷b/b-a其中a=3.b=-2

Answer 1

解：[a/(a²-b²) - 1/(a+b)]÷b/(b-a)
= -[a/(a+b)(a-b)-(a-b)/(a+b)(a-b)] × (a-b)/b
= -b/(a+b)(a-b) × (a-b)/b
= -1/(a+b)
当a = 3，b = -2时
原式= -1/(3 - 2)
= -1

Answer 2

(a/a的平方-b的平方-1/a+b)÷b/b-a
=a/(a²-b²)-1/(a+b)
=a/((a+b)(a-b))-/(a-b/((a+b)(a-b))
=b/((a+b)(a-b))
b/((a+b)(a-b))÷b/(b-a)
=-(a+b)
=-/(3-2)
=-1

Answer 3

[a/(a² - b²) - 1/(a + b)] ÷ b/(b - a)
= [a/(a² - b²) -(a - b)/(a² - b²) ] × (b - a)/b
= b/(a² - b²) × (b - a)/b
= -1/(a + b)
把 a = 3，b = -2代入得：
原式
= -1/(3 - 2)
= -1

Answer 4

[a/(a²-b²) - 1/(a+b)]÷b/(b-a)
= -[a/(a+b)(a-b)-(a-b)/(a+b)(a-b)] × (a-b)/b
= -b/(a+b)(a-b) × (a-b)/b
= -1/(a+b)
接下来代入吧

Answer 5

解：[a/(a² - b²) - 1/(a + b)] ÷ b/(b - a)
= [a/(a² - b²) -(a - b)/(a² - b²) ] × (b - a)/b
= b/(a² - b²) × (b - a)/b
= -1/(a + b)
把a = 3,b = -2代入
原式= -1/(3 - 2)= -1
正规步骤= =