On the basis of the Pythagorean Theorem in the right triangle with sides a, b, c:
a² + b² = c², where c is hypotenuse.
You can drive the triangle a = 3 and b = √2, because √(3²+√2²) = √(9+2) = √11
√2 is hypotenuse of the right triangle with sides a = b = 1.
So, you are construct first the right triangle a=b=1, than a=3, b=√2.