( 1)a-(a-3b+4c)+3(-c+2b)

(2)(3x2-2xy+7)-(-4x2+5xy+6)

(3)2 x2-{-3x+6+[4x 2-(2 x2-3x+2)]]

(2) simplification

( 1)a & gt； 0，b & lt0，|6-5b|-|3a-2b|-|6b- 1|

(2) 1 & lt； a & lt3、| 1-a|+|3-a|+|a-5|

(3) When a= 1, b=-3 and c= 1, find the value of the algebraic formula a2b-[a2b-(5abc-a2c)]-5abc.

(4) When the algebraic expression -(3x+6)2+2 obtains the maximum value, find the value of the algebraic expression 5x-[-x2-(x+2)].

(5) x2-3xy=-5, xy+y2=3, and find the value of x2-2xy+y2.

Practice reference answer:

(1) calculation:

( 1)-a+9 b-7c(2)7x2-7xy+ 1(3)-4

(2) simplification

( 1)∵a & gt； 0，b & lt0

∴|6-5b|-|3a-2b|-|6b- 1|

=6-5b-(3a-2b)-( 1-6b)

= 6-5 b-3a+2 b- 1+6b =-3a+3 b+5

(2)∵ 1 & lt； A< three

∴| 1-a|+|3-a|+|a-5|=a- 1+3-a+5-a=-a+7

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