##### Need algebra help to write the equation of a line

label Algebra
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write the equation of a line the passes through the point (7,-2) and is perpendicular to the line x+3y=15

Nov 12th, 2015

Since the problem statement only gives us one point, we need to use point-slope form to find the equation of this line, instead of two-point form. Since we have the point (7,-2), we need to figure out what the slope of the line needs to be. If our line needs to be perpendicular to the line given in the problem statement, first we need to figure out the slope of THAT line. The equation of that line is x+3y=15, or y = -(1/3)x + 5. The slope of the line is -1/3. A perpendicular line must have a slope that is the negative reciprocal of -1/3, thus the slope must be 3.

Now we know that our line must go through the point (7,-2) and should have a slope 3. We can use point-slope form: y-y1 = m(x-x1), where y1 = -2, x1 = 7, and m = 3. We have y+2 = 4(x-7), or y + 2 = 4x - 28, or y = 4x - 30, which is the solution.

Nov 12th, 2015

where did you get the 4?  you put the m=3 and then put y+2=4(x-7). how did you get the 4?

Nov 12th, 2015

where did you get the 4?  you put the m=3 and then put y+2=4(x-7). how did you get the 4?

Nov 12th, 2015
where did you get the 4? you put the m=3 and then put y+2=4(x-7). how did you get the 4?
Nov 12th, 2015

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Nov 12th, 2015
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Nov 12th, 2015
Oct 21st, 2017
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