SOLUTION: What describes the lines represented by these equations? X+y=9 X-y=9

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Question 807734: What describes the lines represented by these equations?
X+y=9
X-y=9

Answer by TimothyLamb(4379)   (Show Source): You can put this solution on YOUR website!
Converting these lines to slope-intercept form: y = mx + b
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L1: y = -x + 9
L2: y = x - 9
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we can say that the lines are perpendicular, because their slopes are negative reciprocal: 1/1 and -1/1
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Also, L1 and L2 intersect at (9, 0)
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We can see this by substituting (x - 9) for y in L1 and solving for x (x=9), then substituting x=9 into either equation to find y=0.
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