Diagonal of the square =√2 a
⇒√2 a =12√2
⇒a=12
so the perimeter of the square =4*12=48cm
perimter of the triangle is also 48 cm...
so each side of the triangle is 16cm
area of the eq. triangle =√3 a²/4
so the are of the triangle=√3*64=64√3 cm²