Answer
$f(x)=-3x^2$
Work Step by Step
Since the shape of the graph is a $f(x) = x^2$ we will start with that function:
$f(x)=x^2$
The first thing to notice is the graph is reflected across the x-axis. The reflection across the x-axis means multiply the right side by -1
$f(x)=-x^2$
The second thing to notice is the graph is stretched vertically by a factor of 3 because $f(x)=-x^2$ passes through (1,-1) but the graph goes through (1,-3). To apply vertical stretches, multiply the right side by the factor.
$f(x)=-3x^2$
