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What two criteria are needed for triangles to be similar

Which of these equations, when solved, gives a different value of x than the other three? a9.1 = -0.2x + 10 b10 = 9.1 + 0.2x c10 – 0.2x = 9.1 d9.1 – 10 = 0.2x

Write an equation for the function that includes the points (1,4/5) and (2,2/3)