To write the equation in standard form rearrange to this form ax^2 + bx + c = 0. Rearrange the equation 2x^2 + 7x = 15 by subtracting 15 from both sides.
2x^2 + 7x - 15 = 0
The left side factors into (2x - 3)(x + 5) since it multiplies to 2x^2 - 3x + 10x - 15 = 2x^2 + 7x - 15.
When you plot the three points on the graph it makes a triangle. As it rotates around the x axis, the points at 2,0 and 2,-2 make a circle, which becomes the base of the cone.
