Do it like this one:
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Show how you use matrices to write an equation for a line that passes through the following points:
(-7, 9), (8, 9)
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| x y 1|
|-7 9 1| = 0
| 8 9 1|
x*(9-9) - y*(-7-8) + 1*(-7*9 - 8*9) = 0
15y -135 = 0
y = 9
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| x y 1|
| 4 -10 1| = 0
| 1 1 1|
x*(-10*1 - 1*1) - y*(4*1 - 1*1) + 1*(4*1 - 1*-10) = 0
-11x -3y + 14 = 0
11x + 3y = 14
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