To find the missing side using the Pythagorean theorem, which states that in a right-angled triangle, the square of the hypotenuse is equal to the sum of the squares of the other two sides.
In this case, we have two sides with lengths of 11cm and 4cm, and we need to find the length of the missing side, which we'll call "c".
We can use the formula c^2 = a^2 + b^2, where "a" and "b" are the lengths of the two known sides and "c" is the length of the missing side.
Plugging in the values, we get:
c^2 = 11^2 + 4^2
c^2 = 121 + 16
c^2 = 137
Taking the square root of both sides, we get:
c = √137
So the missing side of the triangle is approximately 11.7cm (rounded to one decimal place).