Explanation:
we create 2 equations with 2 variables by using the given point coordinates in both :
A×1 + B×-2 = 7
A - 2B = 7
A×1 - B×-2 = 3
A + 2B = 3
to solve we can simply add both equations to temporarily eliminate B and solve for A :
A - 2B = 7
A + 2B = 3
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2A 0 = 10
A = 10/2 = 5
now, we use one of the original equations to solve for B :
5 + 2B = 3
2B = -2
B = -2/2 = -1