maths about form3

用戶19864

2008-04-12 9:46 pm

1.Given that straight lines L1 and L2 are perpendicular to each other , if
the slope of L1 is -3 and L2 passes through P(6.-1) and Q(2k, -6), find the
value of a.

2.It is given that L1 and L2 are the graphs of the equations 3x-6y=0 and
x-2y+8=0 respectively.
(a)If (2,a) and (-4,b) are points on L1, find the values of a and b.

回答 (1)

用戶8672

2008-04-12 11:07 pm

✔ 最佳答案

1. [ are you asking the value of k ?? ]

Slope L1 X Slope L2 = -1
Slope L2 = -1 / -3 = 1/3

Consider L2 ,

[(-6) - (-1)] / 2k-6 = 1/3
-5 / 2k-6 = 1/3
[ 用交义相乘method]
-5 x 3 = 2k - 6
- 15 = 2k - 6
k = - 4.5
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2. Sub ( 2, a ) and ( -4, b) into the equation of L1, we have ,

3(2) - 6 a = 0
6-6 a = 0
a = 1

3(-4) - 6 b = 0
-12 - 6 b = 0
b = -2

2008-04-12 15:13:43 補充：
001 的1. 答案錯了..

[(-6) - (-1)] / 2k-6 = 1/3 才對

[6 ﹣(-1)] / (2k ﹣6) = 1 / 3 是錯的!

因為 y2 - y1 / x2 - x1 = slope

given 左P(6.-1) and Q(2k, -6)
y2 係 - 6 唔係 6 呀!

參考: myself :)

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