1.find the range of value of k such that the quadratic equation
x^2 +2x-k=2 has real roots.
2.It is given that x varies directly as y and inversely as z^2. If y is decreased by 10% and z is increased by 20%,then X is decreased by?
3.If the simultaneous equations y=4x,y=kx^2+1 have only one solution,
find the value of k
幾條maths問題
2009-07-08 3:06 am
回答 (2)
2009-07-08 3:21 am
✔ 最佳答案
1 Discriminent>=0=>2^2-4(-k-2)>0
4+4(k+2)>0
k+2>-1
k>-3
2 Let x=Ky/z^2=>K=xz^2/y...(1)
new y=y'=0.9y,new z=z'=1.2z
Substitute into (1) K=(x')(z'^2)/(y')
=> xz^2/y=(x')(z'^2)/(y')
=> xz^2/y=(x')(1.44z^2)/(0.9y)
x=1.6x'
x'=0.625x
So x is decreased by 37.5%
3 y=4x,y=kx^2+1 have only one solution
So kx^2+1=4x has only one solution
Discriminent=0
16-4k=0
k=4
2009-07-08 3:19 am
1.k>=-3
2.37.5%
3.k=4
2.37.5%
3.k=4
收錄日期: 2021-04-23 20:39:00
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20090707000051KK01892