SOLUTION: A general equation of the family of lines perpendicular to 2x-5y=7 is... THE ANSWER IS: 5x+2y=k (BUT HOW DO U GET THIS?) please tell me how and why this is the answer YOUR HE

Algebra ->  Algebra  -> Coordinate-system -> SOLUTION: A general equation of the family of lines perpendicular to 2x-5y=7 is... THE ANSWER IS: 5x+2y=k (BUT HOW DO U GET THIS?) please tell me how and why this is the answer YOUR HE      Log On

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Question 38647: A general equation of the family of lines perpendicular to 2x-5y=7 is...
THE ANSWER IS: 5x+2y=k (BUT HOW DO U GET THIS?) please tell me how and why this is the answer
YOUR HELP IS MOST APPRECIATED, THANK YOU SO MUCH

Answer by Earlsdon(6103) About Me  (Show Source):
You can put this solution on YOUR website!
Start by putting the given equation in the slope-intercept form: y+=+mx+%2B+b
2x-5y+=+7 --> y+=+%282%2F5%29x+-+7%2F5 You can see that the slope, m, of the given line is 2%2F5
Now you want the family of lines that are perpendicular to this line, and as you know, perpendicular lines will have a slope that is the negative reciprocal of the given line...so the slope of the perpendicular lines will be the negative reciprocal of m+=+2%2F5 or m+=+-%285%2F2%29
Since you are looking for the family of lines, you don't really care where these lines intercept the y-axis, so the y-intercept, b, can be any real number.
So now we have, in the slope-intercept form, the equation for the family of lines perpendicular to the given line:
y+=+-%285%2F2%29x+%2B+b Where b, the y-intercept is any real number. Now if you rearrange this equation:
y+=+-%285%2F2%29x+%2B+b Multiply both sides by 2 to clear the fraction.
2y+=+-5x+%2B+2b Add 5x to both sides.
5x+%2B+2y+=+2b But since b is any real number, so 2b is any real number so you can let 2b = k, so finally you have:
5x+%2B+2y+=+k.