Let the side of square be 422−l and side of triangle be 3l ,
So, total area is given by Δ=43(3l)2+(422−l)2
⇒Δ=1231⋅l2+161(22−l)2
Differentiating with respect to l to get maxima and minima points,
⇒dldΔ=631⋅l−81(22−l)=0 ⇒l=4+33663
Alsodl2d2Δ=631+81 (+ve. which is case of minima)
So, side of triangle will be =3l=4+33223=43+966