又問數啦我=[ [複製鏈接]

it is give that the graph of y =mx^2+8x-1 touches the x-axis at only one point.

find the x-intercept of the graph.

點解我搵到1/-16既 =[
明明答案係1/4 =[

方法一:直接搵VERTEX(好煩唔想計)

方法二:
AS there is only 1 sol
therefore delta=0
b^2-4ac=0
64+4m=0
m=-16

therefore Y=-16x^2+8x-1
solve -16x^2+8x-1=0
(4X-1)^2=0
X=0.25

minor野(關英文事)

打錯題目?


應該係it is given that而不是 it is give that

引用第1樓牙宇於2010-11-09 22:48發表的  :
方法一:直接搵VERTEX(好煩唔想計)
方法二:
AS there is only 1 sol
therefore delta=0
.......

用Since代替As會否更好?
∵ y touches x-axis
∴△=b^2-4ac=0
<=> m=-16

At x-axis, y=0 (optional)
<=> y=-16x^2+8x-1=0
<=> (4x-1)^2=0
<=> x = 1/4 (repeated)

ps舊高中寫法,唔岩新高中的話別插我