mx² - (3m+2)x + 2m+2 = 0
(x - 1)[ mx - (2m+2)] = 0
x = 1 或 x = 2 + 2/m
x₁ < x₂
∴x₁ = 1,x₂ = 2 + 2/m
y = 7x₁ - mx₂
= 7 - m(2 + 2/m)
= 5 - 2m