Question

Write the equation of the quadratic function with roots -2 and 4 and a vertex at (1, 9).

Answer 1

y=(x+2)(x-4)
When x=1, y=9
Sub into the equation x=1 and y=9
\[(1+2)(1-4)=9\]
\[(3)(-3)=9\]
\[-9=9\]
The LHS(Left Hand Side) must equal the RHS(Right Hand Side).
That means you have to multiply -9 by -1.
Therefore the equation would have a minus sign in front of the equation.
\[y=-(x+2)(x-4)\]