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jaytan36

Three points A,B,C with coordinates (2,7) , (1,0) , (5,8) respectively.The point D is the foot of the perpendicular line from A to BC.
Calculate the coordinates D.

jaytan36

Can anybody solve this question

PLEASE

TALL

coordinates D=（5/2，6）
对吗？

乙劍真人

coordinates D=（5/2，6）
对吗？
TALL 发表于 23-6-2011 02:31 PM

应该是 （4，6）..

Log

回复 1# jaytan36
先skecth triangle 出来 so you can know where are the points located .
然后,你发现 line AD and BC tntersect at D. so 你要找 它们的equations and solve simultaneously to get D

gradient line BC, m = (8-0)/(5-1)=2
   equation line BC is
    y-y1=m(x-x1)
       y-0=2(x-1)
       y-2x-2   .---------(1)

gradient  line AD =m'
since D is the foot of the perpendicular line from A to BC that mean AD is perpendicular to line BC
so             m . m' = -1
                  2m'= -1
                    m' = -1/2
  equation line AD is
y-y1=m'(x-x1)
y-7  = -1/2(x-2)
     y  = (-1/2)x +8 --------(2)
solve (1) and (2) simultaneously , u get  x=4, y=6
so D= (4,6)

TALL

回复 4# 乙劍真人


    我用画的，是画到（4，6）
不过算却算到（5/2,6）
难道我算错了？

TALL

回复  jaytan36
先skecth triangle 出来 so you can know where are the points located .
然后,你发现  ...
Log 发表于 23-6-2011 03:01 PM

    确实算错了。。。

jaytan36

谢谢你们

答案是 (4,6)

jaytan36

Another question

Find the area of the triangle which is surrounded by the straight line 3x + 4y = 12, x-axis and y-axis

乙劍真人

Find the area of the triangle which is surrounded by the straight line 3x + 4y = 12, x-axis and y-axis.
jaytan36 发表于 23-6-2011 10:17 PM

jaytan36

谢谢 乙劍真人

乙劍真人

谢谢 乙劍真人
jaytan36 发表于 24-6-2011 02:21 PM

不必客气，祝学习愉快，加油..^^

jaytan36

Three vertices of a triangle are A(1,-1) , B(4,3) , C(2,6) respectively.
Find the equation of the medians of the triangle.

PLEASE HELP