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化简求值(1)(9a2-12ab+5b2)-(7a2+12ab+7b2)...

(1)原式=9a2-12ab+5b2-7a2-12ab-7b2=(9-7)a2+(-12-12)ab+(5-7)b2=2a2-24ab-2b2,当中a=12,b=12时,原式=2×(12)2-24×12×12-2×(12)2,=2×14-6-12=12-6-12=-6.(2)∵|x+2|+(3x-2)2=0,∴x+2=0,3y-2=0,∴x=-2,y=23,原式=12x-2x+...

原式=9a2-12ab+5b2-7a2+12ab-7b2=2a2-2b2,当a=12,b=-1时,原式=2×14-2×1=-32.

(1)原式=9a 2 -12ab+5b 2 -7a 2 -12ab-7b 2 =(9-7)a 2 +(-12-12)ab+(5-7)b 2 =2a 2 -24ab-2b 2 ,当中 a= 1 2 ,b= 1 2 时,原式=2×( 1 2 ) 2 -24× 1 2 × 1 2 -2×( 1 2 ) 2 ,=2× 1 4 -6- 1 2 = 1 2 -6- 1 2 =-6.(2)∵|x+2|+(3x...

原式=3a2b-4ab2+2(2ab-3a2b)-2ab+3ab2=3a2b-4ab2+4ab-6a2b-2ab+3ab2=-3a2b-ab2+2ab,∵a=12,b=2,∴原式=3×14×2-12×4+2=?32.

(1)原式=-2a2-4a-4,当a=-12时,原式=-12+2-4=-52;(2)原式=94ab-5a2b-5,当a=1,b=-2时,原式=-92+10-5=12;(3)原式=a2-b2-2ab,∵a2-b2=2,ab=-3,∴原式=2+6=8.

原式=ab+3a2-2a2+4ab-3ab=a2+2ab,当a=-1,b=-12时,原式=1+1=2.

原式=5ab-6ab+8ab2+12ab-5ab2=-12ab+3ab2,当a=12,b=-23时,原式=16+23=56.

原式=9a2-12ab-a2+4a+6ab=8a2-6ab+4a,当a=-2,b=-12时,原式=32-6-8=18.

(1)原式=(3a2b+5a2b)+(2ab2-4ab2)+7-4,=8a2b-22ab2+3.(2)原式=4x2y-[6xy-8xy+4-x2y]+1,=4x2y-6xy+8xy-4+x2y+1,=5x2y+2xy-3,当x=-12,y=4时,原式=5×(12)2×4-2×(-12)×4=9.

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