搜搜考试网【初2】几道数学题目````高手速度做答```````
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【初2】几道数学题目````高手速度做答```````
1'分解固式(1-a)mn+a-1=
2'若18x^2+19x+m=(9x+5)(2x+n),则m=?n=?
3'若关于x的三次二项式2x^2+mx+n因式分解的结果为(2x-1)(x+1/4),求m,n的植.
4'两个小孩的年龄分别是x,y,已知x^2+xy=99,求这两个孩子的年龄.(过程)尽量让我懂哈````!
过程`````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````
1'分解固式(1-a)mn+a-1=
2'若18x^2+19x+m=(9x+5)(2x+n),则m=?n=?
3'若关于x的三次二项式2x^2+mx+n因式分解的结果为(2x-1)(x+1/4),求m,n的植.
4'两个小孩的年龄分别是x,y,已知x^2+xy=99,求这两个孩子的年龄.(过程)尽量让我懂哈````!
过程`````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````
1.提取公因式
(1-a)mn+a-1
=(1-a)mn-(1-a)
=(1-a)(mn-1)
2 .18x^2+19x+m
=(9x+5)(2x+n)
=18x^2+(10+9n)x+5n
等号两边对应的各项系数及常数项相等
所以 :19=10+9n
m=5n
解得n=1,m=5
3 .(2x-1)(x+1/4)=2x^2+x*1/2-x-(1/4)
=2x^2-x/2-(1/4)
等号两边对应的各项系数及常数项相等
m=-1/2 n=-1/4
4 .x^2+xy=99
x^2+xy=x(x+y)
99=9*(9+2)
对应项相等 所以:x=9,y=2
(1-a)mn+a-1
=(1-a)mn-(1-a)
=(1-a)(mn-1)
2 .18x^2+19x+m
=(9x+5)(2x+n)
=18x^2+(10+9n)x+5n
等号两边对应的各项系数及常数项相等
所以 :19=10+9n
m=5n
解得n=1,m=5
3 .(2x-1)(x+1/4)=2x^2+x*1/2-x-(1/4)
=2x^2-x/2-(1/4)
等号两边对应的各项系数及常数项相等
m=-1/2 n=-1/4
4 .x^2+xy=99
x^2+xy=x(x+y)
99=9*(9+2)
对应项相等 所以:x=9,y=2