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I have trouble finding the solution for this: Find the equation of the line through (2,a) and (4,b).

• math -

slope = (b-a)/2

using (2,a)
y-a = (b-a)/2 (x-2)
times 2
2y - 2a = (b-a)(x-2)
2y - 2a = bx - 2b - ax + 2a

ax - bx + 2y = 4a - 2b
(a-b)x + 2y = 4a - 2b

check if point not used lies on it ....

LS= (a-b)(4) + 2(b)
= 4a - 4b + 2b
= 4a - 2b
= RS

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