(40) maths question. plz help
回答 (2)
2007-10-29 11:34 am
✔ 最佳答案
Because: y=kx^2 + 3x + 1 touch the x-axis, so, y= 0A= coefficient of x^2
B= coefficient of x
C= coefficient of (x^0=1)
0= B^2 - (4) (A) (C)
0=(+3)^2 - (4) (k) (1)
0=9- 4k
4k=9
k= 9/4 =2.25
Hence, the value of k is 2.25.
參考: Myself
2007-10-29 11:41 am
consider discriminant of the equation, if it touches the x-axis then this implies there is a double root and therefore the discriminant will be zero .
in equation ax^2+bx+c = 0, discriminant is b^2-4ac
=> 3^2-4(k)(1) = 0
=> 9-4k = 0
=> k = 9/4
in equation ax^2+bx+c = 0, discriminant is b^2-4ac
=> 3^2-4(k)(1) = 0
=> 9-4k = 0
=> k = 9/4
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