If two lines represented by ${\mathrm{x}}^4+{\mathrm{x}}^3\mathrm{y}+{\mathrm{cx}}^2{\mathrm{y}}^2-{\mathrm{xy}}^3+{\mathrm{y}}^4=0$ bisect the angle between the other two, then the value of ‘c’ is______

Product of the slopes = –1
Let the equation of one pair be
$\begin{array}{l}{\mathrm{ax}}^2+2\mathrm{hxy}-{\mathrm{ay}}^2=0,\frac{{\mathrm{x}}^2-{\mathrm{y}}^2}{2\mathrm{a}}=\frac{\mathrm{xy}}{\mathrm{h}}\\ ={\mathrm{x}}^4+{\mathrm{x}}^3\mathrm{y}+{\mathrm{cx}}^2{\mathrm{y}}^2-{\mathrm{xy}}^3+{\mathrm{y}}^4\\ =\left({\mathrm{ax}}^2+2\mathrm{hxy}-{\mathrm{ay}}^2\right)\left({\mathrm{hx}}^2-2\mathrm{axy}-{\mathrm{hy}}^2\right)\\ \Rightarrow \mathrm{ah}=1\text{ and }\mathrm{c}=-6\cdot \mathrm{ah}=-6\end{array}$