SOLUTION: How should i start. The below problem seem easy but i not able to solve it. ABCD is parallelogram. A(1,2),B(7,-1), C(-1,-2) and D(x,y). Find equation AD and also CD. C.M

Question 511385: How should i start. The below problem seem easy but i not able to solve it.
ABCD is parallelogram. A(1,2),B(7,-1), C(-1,-2) and D(x,y). Find equation AD and also CD.

C.M
Answer by mananth(16946) (Show Source): You can put this solution on YOUR website!
A(1,2),B(7,-1), C(-1,-2) and D(x,y)
In any parallelogram ABCD AB || to CD so CD has the same slope as AB and passes through C (-1-2)
x1 y1 x2 y2
1 2 7 -1

slope m = (y2-y1)/(x2-x1)
( -1 - 2 )/( 7 - 1 )
( -3 / 6 )
m= - 1/ 2

Plug value of the slope and point (-1 ,-2) in
Y = m x + b
-2.00 = 1/2 + b
b= -2 - 1/2
b= -5/ 2
So the equation will be
Y = - 1/2 x -5/2 is the equation of CD
....
In any parallelogram ABCD BC || to AD so AD has the same slope as BC and passes through A (1,2)
x1 y1 x2 y2
7 -1 -1 2

slope m = (y2-y1)/(x2-x1)
( 2 - -1 )/( -1 - 7 )
( 3 / -8 )
m= - 3/ 8

Plug value of the slope and point ( 1 , 2 ) in
Y = m x + b
2.00 = - 3/8 + b
b= 2 - - 3/8
b= 19/ 8
So the equation will be
Y = - 3/8 x + 19/8
m.ananth@hotmail.ca

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