Binary form
= Binary form
{title2=$f(x,y)=\sum_{i=0}^d\binom di f_i x^{d-i}y^i$}
A binary form is a homogeneous polynomial in two variables. Degree-$d$ binary forms give the symmetric-power representation of the standard two-dimensional representation of $SL_2$, after using its invariant alternating form to identify the standard representation with its dual.