Question

已知A=

1

x-2

，B=

2

x2-4

，C=

x

x+2

．将它们组合成（A-B）÷C或A-B÷C的形式，请你从中任选一种进行计算，先化简，再求值其中x=3．

Answer 1

选一：（A-B）÷C=(

1

x-2

-

2

x2-4

)÷

x

x+2

=

x

(x+2)(x-2)

×

x+2

x

=

1

x-2

．
当x=3时，原式=

1

3-2

=1；
选二：A-B÷C=

1

x-2

-

2

x2-4

÷

x

x+2

=

1

x-2

-

2

(x+2)(x-2)

×

x+2

x

=

1

x-2

-

2

x(x-2)

=

x-2

x(x-2)

=

1

x

．
当x=3时，原式=

1

3

．