Question 975247
I'm assuming you need real coefficients so you use complex conjugate roots.
{{{y=a(x-i)(x+i)(x-2i)(x+2i)}}}
{{{y=a(x^2+1)(x^2+4)}}}
{{{y=a(x^4+4x^2+x^2+4)}}}
{{{y=a(x^4+5x^2+4)}}}
When {{{x=-1}}}, {{{y=20}}}
{{{20=a((-1)^4+5(-1)^2+4)}}}
{{{20=a(1+5+4)}}}
{{{20=a(10)}}}
{{{a=2}}}
So,
{{{highlight(y=2x^4+10x^2+8)}}}

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*[illustration ZZ4.JPG].