Question

计算：
①

y

7x

÷(-

2

x

)
②

a-2

a-1

-

2a-3

a-1

③

12

m2-9

-

2

m-3

④

x2

x-1

-x-1．

Answer 1

①

y

7x

÷（-

2

x

）=

y

7x

×（-

x

2

）=-

y

14

；

②原式=

a-2-(2a-3)

a-1

=

a-2-2a+3

a-1

=

-a+1

a-1

=

-(a-1)

a-1

=-1；

③原式=

12

(m-3)(m+3)

-

2(m+3)

(m-3)(m+3)

=

12-(2m+6)

(m-3)(m+3)

=

-2m+6

(m-3)(m+3)

=

-2(m-3)

(m-3)(m+3)

=-

2

m+3

；

④原式=

x2

x-1

-

(x-1)2

x-1

=

x2-(x2-2x+1)

x-1

=

x2-x2+2x-1

x-1

=

2x-1

x-1

．