搜狗做题网先化解,再求值：【1/(x2+3x+2)+1/(x2+5x+6)+1/(x2+7x+12)】/1/(x2+9x+20),
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先化解,再求值：【1/(x2+3x+2)+1/(x2+5x+6)+1/(x2+7x+12)】/1/(x2+9x+20),其中x=√2
原式=[1/(x+1)(x+2)+1/(x+2)(x+3)+1/(x+3)(x+4)] ×(x+4)(x+5)
=[1/(x+1)-1/(x+2) +1/(x+2)-1/(x+3) +1/(x+3)-1/(x+4)]×(x+4)(x+5)
= [1/(x+1)-1/(x+4)]×(x+4)(x+5)
=3/(x+1)(x+4)×(x+4)(x+5)
=3(x+5)/(x+1)
当x=√2时
=3(√2+5)/(√2+1)
=3(√2+5)(√2-1)
=3(2-√2+5√2-5)
=12√2 -9
=[1/(x+1)-1/(x+2) +1/(x+2)-1/(x+3) +1/(x+3)-1/(x+4)]×(x+4)(x+5)
= [1/(x+1)-1/(x+4)]×(x+4)(x+5)
=3/(x+1)(x+4)×(x+4)(x+5)
=3(x+5)/(x+1)
当x=√2时
=3(√2+5)/(√2+1)
=3(√2+5)(√2-1)
=3(2-√2+5√2-5)
=12√2 -9
先化解,再求值：【1/(x2+3x+2)+1/(x2+5x+6)+1/(x2+7x+12)】/1/(x2+9x+20),
解方程：1/x2+x +1/x2+3x+2 +1/x2+5x+6 +1/x2+7x+12 +1/x2+9x+20=5/x
先化解,在求值,(2x-x+1分子x2-2x)÷x2-4x分子x2-16,其中x满足3x2-x-1=0,在线等,求好心人
先化简，再求值：9x+6x2-3(x-23x2)，其中x=-1．
(x2+3x+9)/(x2-27)+(6x)/(9x-x2)-(x-1)/(6+2x)
先化简，再求值：(x+2x2-2x-x-1x2-4x+4)÷x2-16x2+4x，其中x=2+3．
1/(x2+3x+2)+1/(x2+5x+6)+1/(x2+7x+12)=1/(x+4)
先化简,再求值:(1)2x2-5x x2 4x,其中x=-3 (2)(3x2-xy-2y2)-2(x2 xy-2y2),
1/(x2+x)+1/(x2+3x+2)+1/(x2+5x+6)+1/(x2+7x+12)=4/21
x2+3x+9/x2-27+6x/9x-x2-x-1/6+2x 化简
化简x2+3x+9/x2-27+6x/9x-x2-x-1/6+2x
解方程：X2--1/8(X2+2X)+X2+2X/3(X2--1)=11