How to graph a parabola y=1/2(x+1)(x-5)?

1 Answer
May 12, 2015

From the formula y = (1/2)(x+1)(x-5), we can tell several things:

The coefficient of x^2 is positive, so the parabola is upright, shaped a bit like a U.

The parabola crosses the x-axis where y=0, when x = -1 and x = 5.

The vertex of the parabola will have an x coordinate exactly between these two values x = (-1+5)/2 = 2.

Substituting x = 2 into the formula, we get

y = (1/2)(2+1)(2-5) = (1/2)3(-3) = -9/2 = -4.5

So the vertex of the parabola is at (2, -4.5).

If you want to know any more points through which the parabola passes, choose an x coordinate and substitute it into the formula to get the corresponding y value.