Question 543580: Write an equation in standard form
(Ax+By=C)
Passes through (1,1) and (3,9)
Can you line by line show me how to do this
Answer by Alan3354(69443)   (Show Source):
You can put this solution on YOUR website! Write an equation in standard form
(Ax+By=C)
Passes through (1,1) and (3,9)
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There's more than 1 way to do it.
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The hard way:
Find the slope, m
m = diffy/diffx = (9-1)/(3-1) = 4
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Use the slope and y = mx + b with either point to find b, the y-intercept
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1 = 4*1 + b
b = -3
--> y = 4x - 3
4x - y = 3
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The easy way, using determinants:
|x y 1|
|1 1 1| = 0
|3 9 1|
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x*(1-9) - y*(1-3) + 1*(9-3) = 0
-8x + 2y + 6 = 0
4x - y = 3
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