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(2 )3 ( x + 2) - 2( x - 1) ; 解:原式= 3 x + 6 - 2 x + 2 = x + 8 ; (3) 12 ( x - 4) + 13 ( - 2 x + 3) ; 解:原式= 12 x - 2 - 23 x + 1 =- 16 x - 1 ; (4 )2 a - 3 b + [4 a - (3 a - b )] . 解:原式= 2 a - 3 b + a + b = 3 a - 2 b . 5 .計算 2 a - (2 a - 1) 的結(jié)果是 ( ) A . 1 B . - 1 C . 4 a + 1 D . 4 a - 1 6 .下列運算正確的是 ( ) A .- 2( a - b ) =- 2 a - b B . - 2( a - b ) =- 2 a + b C .- 2( a - b ) =- 2 a - 2 b D . - 2( a - b ) =- 2 a + 2 b 7 .下列各式中,與 a - b - c 的值不相等的是 ( ) A . a - ( b + c ) B . a - ( b - c ) C . ( a - b ) + ( - c ) D . ( - c ) - ( b - a ) A D B 8 .將多項式 3 x3- 2 x2+ 4 x - 5 添括號,正確的是 ( ) A . 3 x3- (2 x2+ 4 x - 5) B . 2 x2+ (3 x3+ 4 x - 5) C . (3 x3- 5) + ( - 2 x2- 4 x ) D . (3 x3+ 4 x