Question 890474
Generically,
{{{(px+qy)(rx+sy)=ax^2+2hxy+by^2}}}
{{{prx^2+psxy+qrxy+qsy^2=ax^2+2hxy+by^2}}}
{{{prx^2+(ps+qr)xy+qsy^2=ax^2+2hxy+by^2}}}
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.
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{{{a=pr}}}
{{{2h=ps+qr}}}
{{{b=qs}}}