Posted by luckybee on Sunday, February 19, 2012 at 5:17pm.
please check my homework
given P(7,2) and the line y + 3x=7 find the equation for the line
parallel line: y+3x+7
y-2==1/3x + 14
y=1/3x + 14 +2
parallell and perpendicular lines - Reiny, Sunday, February 19, 2012 at 5:41pm
Here is a neat way to do these question in a quicker way
You should have learned that for a straight line equation in the form
Ax + By = C, the slope of the line is -A/B
so for 3x+y = 7 , a parallel line will differ only in the C value
so new equation is
3x + y = C
plug in the point (7,2)
21 + 2 = C = 23
so new equation: 3x + y = 23 or y = -3x - 23
notice the given point does not even satisfy your final equation.
Your error is in the 2nd line, should be
y = -3(x-7) + 2
For the perpendicular short cut way:
slope of given equation is -3
so slope of perpendicular line is +1/3
x - 3y = C, plug in the point (7,2)
7 - 6 = C = 1
x - 3y = 1 or y = (1/3)x - 1/3
again, you made the error in the 2nd line, it should say
y-2 = (1/3)(x-7)
then 3y - 6 = x-7
x - 3y = 1 , the same result as mine
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