##= color(purple)(6cm^2##
A very frequently observed Pythagorean triplet is :
##color(red)(3,4,5##
This triplet perfectly fits the conditions provided in the question as :
- Perimeter : ##3+4+5 = 12cm##
- and, ##5cm## perfectly fits as the hypotenuse(as it is the largest of all sides)
So it is a right angled triangle of base and height: ##3,4##
Area of a right angled triangle :
##color(purple)(area = 1/2##(base.height)
##= 1/2(3.4)##
##= color(purple)(6cm^2##