suppose i'm asked to find the associated bilinear form for the quadratic form $\displaystyle q(v)=x_1x_3+x_2^2,$ wonder if i first need to find the associated matrix to this quadratic form, then in order to get the associated bilinear form i'd do $\displaystyle f\big((x_1,x_2,x_3),(y_1,y_2,y_3)\big)=(x_1~x_2~x_ 3)[\text{matrix of the quadratic form}](y_1~y_2~y_3)^t$ ?