先化简,再求值: x 2 + 2 x + 1 x 3 − x ÷ ( 1 + 1 x ) ,其中 x = 3 + 1 .
( 998 ) 2
a - b 2 - a a - 2 b
( 9 x 4 - 15 x 2 + 6 x ) ÷ 3 x
1 2 x ( 2 x 2 - 4 x + 6 )
2 m + n 2 m - n