Question 983276
{{{y=3-15x-3x^2}}}
{{{y/(-3)=x^2+5x-1}}}
{{{y/(-3)=x^2+5x+(5/2)^2-25/4-1}}}
{{{y/(-3)=(x+5/2)^2-25/4-1}}}
{{{y/(-3)=(x+5/2)^2-29/4}}}
{{{y=(-3)(x+5/2)^2-3(-29/4)}}}
{{{y=(-3)(x+5/2)^2+87/4}}}
Is this what you wanted?