SOLUTION: ABCD is a rectangle/ The coordinates of A and B are (1,4) and (5,2) respsectively. The x-coordinate of D is -2. Find: a) the equation of AD b) the y-coordinate of D c) the coord

Algebra ->  Linear-equations -> SOLUTION: ABCD is a rectangle/ The coordinates of A and B are (1,4) and (5,2) respsectively. The x-coordinate of D is -2. Find: a) the equation of AD b) the y-coordinate of D c) the coord      Log On


   



Question 1123947: ABCD is a rectangle/ The coordinates of A and B are (1,4) and (5,2) respsectively. The x-coordinate of D is -2. Find:
a) the equation of AD
b) the y-coordinate of D
c) the coordinates of C

Answer by MathLover1(20855) About Me  (Show Source):
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ABCD is a rectangle
The coordinates of A and B are (1,4) and (5,2) respectively.
The x-coordinate of D is -2. -> D is at (-2,y)

Find:
a) the equation of AD
we will first find a slope of line that contaisAB, a line that is perpendicular to the line that contains AD :

use given points (1,4) and (5,2) to find slope m
m=%28y%5B2%5D-y%5B1%5D%29%2F%28x%5B2%5D-x%5B1%5D%29
m=%282-4%29%2F%285-1%29
will have a slope ...use given point that lie on AB (1,4) (
4=2%2A1%2Bb
4-2=b
b=2
and, your equation o the line {{AD}}} is: y=2x%2B2

b) the y-coordinate of D
to find it, use y=2%29x%2B2 and (-2,y)
y=2%28-2%29%2B2
y=-4%2B2
y=-2
so,D is at (-2,-2)

c) the coordinates of C+
point C+ is intersection point o the line DC and BC
since the line DC is parallel to the line AB, they have same slope
m=-1%2F2
equation of the line DC is:
y=-%281%2F2%29x%2Bb....use point D which is at (-2,-2)

-2=-%281%2F2%29%28-2%29%2Bb
-2=1%2Bb
-2-1=b
b=-3
y=-%281%2F2%29x-3.....eq.1
and equation of AD has a slope m=2 and is parallel to BC
so,equation of the line BC is:
y=2x%2Bb....use point B which is at (5,2)
2=2%2A5%2Bb
2-10=b
b=-8
and y=2x-8.....eq.2
from eq.1 and eq.2 we have
2x-8=-%281%2F2%29x-3
2x%2B%281%2F2%29x=8-3
2x%2Bx%2F2=5
4x%2Bx=10
5x=10
x=2
go to y=2x-8.....eq.2, plug in x

y=2%2A2-8
y=4-8
y=-4
so, point C+ is at (2,-4)

(1,4) and (5,2)