Question

if the points A(3,5) & B(1,4) lie on the graph of the line ax+by=7, find the values of a and b.

Answer 1

(3,5) --> 3a + 5b = 7
(1,4) --> a + 4b = 7

3a + 5b = 7 | ×1
a + 4b = 7 | ×3
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3a + 5b = 7
3a + 12b = 21 -
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-7b = -14
b = -14 : (-7)
b = 2

a + 4b = 7
a + 4 × 2 = 7
a + 8 = 7
a = 7 - 8
a = -1