If $x^2-3xy+2y^2=0$ represents two sides of triangle and orthocentre is (2, 1) then equation of third side is

Given Equation $x^2-3xy+2y^2=0$

a = 1,  2h = - 3,    b = 2

and orthocentre = (2, 1)=(l,m)

Equation of third side

$\begin{array}{l}lx+my=\frac{a{m}^2-2hlm+b{l}^2}{a+b}\\ 2x+y=\frac{1{\left(1\right)}^2+3\left(2\right)\left(1\right)+2{\left(2\right)}^2}{1+2}\\ \Rightarrow 2x+y=\frac{1+6+8}{3}\\ \Rightarrow 2x+y=5\end{array}$