The given equation corresponds to a parabola:
[tex]y=-2(x-3)^2[/tex]The y-intercept of the parabola is the point when it crosses the y-axis, at this point x=0, to determine this value you have to replace the formula with x=0 and calculate the value of y:
[tex]\begin{gathered} y=-2(0-3)^2 \\ y=-2(-3)^2 \end{gathered}[/tex]Solve the exponent first, then the multiplication
[tex]\begin{gathered} y=-2(-3)^2 \\ y=-2\cdot9 \\ y=-18 \end{gathered}[/tex]The y-intercept for the given function is (0,-18)