1x^4-46x^2+25
=(x^4-10x^2+25)-36x^2
=(x^2-5)^2-(6x)^2
=(x^2+6x-5)(x^2-6x-5)
=(x^2+6x-5)(x-5)(x-1)
=(x+3-√14)(x+3+√14)(x-5)(x-1)
2
(x+y)^2+10(x+y)+25=(x+y+5)^2
3
2x^2+2x+0.5=2(x^2+x+1/4)=2(x+1/2)^2
4
9x^2+16xy+4y^2=16x^2+16xy+4y^2-7x^2
=(4x+2y)^2-7x^2=(4x+2y-√7x)(4x+2y+√7x)
1
分式(x-1)/(2x+1)有意义需2x+1≠0,即x≠-1/2
2
3x+2是分母吧,应该括起来
5/(3x+2)>有意义,
需5/(3x+2)>0==>3x+2>0==》x>-2/3
还有一题,分式乘法:[3(m-n)/xy^2][xy/mn]
[3(m-n)/(xy^2)](xy)/(mn)=[3(m-n)/y*1/(mn)=3(m-n)/(mny)