Question 1126203
{{{y=a(x-(-1))^2-3}}}
{{{y=a(x+1)^2-3}}}
{{{y+3=a(x+1)^2}}}

{{{a=(y+3)/(x+1)^2}}}

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{{{a=(-21+3)/(2+1)^2}}}

{{{a=-18/9}}}

{{{a=-2}}}

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{{{y=-2(x+1)^2-3}}}, which you can 'simplify' .


{{{y=-2(x^2+2x+1)-3}}}

{{{-2x^2-4x-2-3}}}

{{{-2x^2-4x-5}}}, here in ax^2+bx+c  form.