How to prove the equation for maximum height of a projectile from the equation in $Y$?

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I'm having problems to proof the equation for maximum height which is given as follows:

$$H_{\max}=\frac{v_o\sin^2\omega}{2\times g}$$

starting from here (which is the equation for $y$):

$$y=v_{oy}t-\frac{1}{2}gt^2$$

I am confused whether if the speed on $y$-axis becomes $0$ in the maximum height but would not this cancel the first term in the above equation?.

What would be the way to go?

Edit:

Although there can be different ways to assess this situation. What would be the one that explains what is happening to the vectors while the projectile is in the top?

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The vertex of the parabola occurs at $t=-\dfrac{b}{2a} =\dfrac{v_{0y}}{g}$. Substituting $v_{0y}=v_0\sin\omega$ and evaluating the function there should give you what you're after.