搜搜考试网先化简再求值,计算好点的进
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先化简再求值,计算好点的进
3x^y-[2x^2y-(2xy-1/2 x^2)-4x^2]-xy,其中x=2,y=1/3.
(7a^2n -2b^2m+1 +c)-(-2a^2n +4b^2m+1 +c),其中a=1,b=-1,m,n都为正整数.
已知:(a+3)^2 +|b+1|+c^2=0,M=3a^2 b -2ab^2 c-4ab^3,N=3/2 ab^2 c -a^2 b +2ab^3.求M-N的值
忘,
3x^y-[2x^2y-(2xy-1/2 x^2)-4x^2]-xy,其中x=2,y=1/3.
(7a^2n -2b^2m+1 +c)-(-2a^2n +4b^2m+1 +c),其中a=1,b=-1,m,n都为正整数.
已知:(a+3)^2 +|b+1|+c^2=0,M=3a^2 b -2ab^2 c-4ab^3,N=3/2 ab^2 c -a^2 b +2ab^3.求M-N的值
忘,
3x^y-[2x^2y-(2xy-1/2 x^2)-4x^2]-xy
=3x^y-(2x^2y-2xy+1/2 x^2-4x^2)-xy
=3x^y-(2x^2y-2xy-7/2 x^2)-xy
=3x^y-2x^2y+2xy+7/2 x^2-xy
=x^2y+xy+7/2 x^2
=2^2*(1/3)+2*(1/3)+(7/2)*2^2
=4/3+2/3+14
=16
(7a^2n -2b^2m+1 +c)-(-2a^2n +4b^2m+1 +c)
=7a^2n -2b^(2m+1) +c+2a^2n-4b^(2m+1)-c
=9a^2n-6b^(2m+1)
=9*1^2n-6*(-1)^(2m+1)
=9*1-6*(-1)
=15
因为:(a+3)^2≥0,|b+1|≥0,c^2≥0
所以a+3=0,b+1=0,c=0
a=-3,b=-1,c=0
M-N=(3a^2 b -2ab^2 c-4ab^3)-(3/2 ab^2 c -a^2 b +2ab^3)
=3a^2 b -2ab^2 c-4ab^3-3/2 ab^2 c +a^2 b -2ab^3
=4a^2b-7/2 ab^2c-6ab^3
=4*(-3)^2*(-1)-7/2 ab^2*0-6*(-3)*(-1)^3
=-36-0-18
=-54
=3x^y-(2x^2y-2xy+1/2 x^2-4x^2)-xy
=3x^y-(2x^2y-2xy-7/2 x^2)-xy
=3x^y-2x^2y+2xy+7/2 x^2-xy
=x^2y+xy+7/2 x^2
=2^2*(1/3)+2*(1/3)+(7/2)*2^2
=4/3+2/3+14
=16
(7a^2n -2b^2m+1 +c)-(-2a^2n +4b^2m+1 +c)
=7a^2n -2b^(2m+1) +c+2a^2n-4b^(2m+1)-c
=9a^2n-6b^(2m+1)
=9*1^2n-6*(-1)^(2m+1)
=9*1-6*(-1)
=15
因为:(a+3)^2≥0,|b+1|≥0,c^2≥0
所以a+3=0,b+1=0,c=0
a=-3,b=-1,c=0
M-N=(3a^2 b -2ab^2 c-4ab^3)-(3/2 ab^2 c -a^2 b +2ab^3)
=3a^2 b -2ab^2 c-4ab^3-3/2 ab^2 c +a^2 b -2ab^3
=4a^2b-7/2 ab^2c-6ab^3
=4*(-3)^2*(-1)-7/2 ab^2*0-6*(-3)*(-1)^3
=-36-0-18
=-54