Finding the analytic expression of quadratic function （-1,0),(3,0),(1,-5) How can I get the analytic expression

The simplest way is to set it as "two-point formula": let the equation be y = a (x-x1) (x-x2)
The first and second points are y = 0, x = - 1 and x = 3, which are replaced by x 1 = - 1 and x 2 = 3
The third point can be replaced to find a = 4 / 5
Therefore, the analytical formula is y = 4 / 5 (x + 1) (x-3), which is reduced to y = 5 / 4x ^ 2-5 / 2x-15 / 4

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