Persamaan parabola yg melalui titik (1,0) (_5,0) dan (2,7) adalah

y = a(x - x1)(x - x2)
7 = a(2 - 1)(2 - (-5))
7 = a(1)(7)
a = 7/7 = 1
y = a(x - x1)(x - x2)
y = 1(x - 2)(x - (-5))
y = (x - 2)(x + 5)
y = x² + 3x - 10