Wednesday, February 22, 2012

Determine the equation of the line that passes through the point (-2,4) and it is perpendicular to -2x+4y-1=0.

We'll write the equation of the line into the slope
intercept form:


y=mx+n, where m is the slope of the line
and n is the y intercept.


We need to put the equations
in this form to determine their slopes. We'll use the property of slopes of 2
perpendicular lines: the product of the values of the slopes of 2 perpendicular lines is
-1.


Let's suppose that the 2 slopes are m1 and
m2.


m1*m2=-1


We'll
determine m1 from the given equation of the line, that is perpendicular to the one with
the unknown equation.


The equation is
-2x+4y-1=0.


We'll isolate 4y to the left side. For this
reason, we'll subtract -2x - 1 both sides:


4y = 2x +
1


We'll divide by 4:


y = x/2
+ 1/4


The slope m1 =
1/2.


(1/2)*m2=-1


m2=-2


We
also know that the line passes through the point (-2,4), so the equation of a line that
passes throuh a given point and it has a known slope
is:


(y-y1)=m(x-x1)


(y-4)=(-2)*(x+2)


We'll
remove the brackets and we'll move all terms to one side:


y
- 4 + 2x + 4 = 0


We'll eliminate like terms and we'll get
the equation of the requested line:


y + 2x =
0

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