Tuesday, November 16, 2010

Given the point (2, -1) and the line 2y+4x-8=0, what is the line parallel to it and that passes through (2,-1)?

If 2 lines are parallel, their slopes have to be
equal.


We'll put the given equation of the line in the
point slope form.


y = mx +
n


For this reason, we'll have to isolate y to the left side
and we'll subtract 4x both sides:


2y = 8 -
4x


We'll divide by 2:


y = -2x
+ 4


Comparing, we'll get the slope of the first line: m1 =
-2


The slope of the parallel line is m2 =
-2.


The line is passing through the point  (2 , -1). The
equation of the parallel line is:


y + 1 = -2(x -
2)


We'll subtract 1:


y = -2(x
- 2) - 1


We'll remove the
brackets:


y = -2x + 4  -
1


We'll combine like terms:


y
= -2x + 3


The equation of the parallel line
is:


y = -2x +
3

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