Answer:
Error was CHOOSING the CORRECT hypotenuse in the given sides.
H = 41 units
Explanation:
Here, the given sides of the triangle are: 41,40 and 9
Now, as we know in a RIGHT ANGLED TRIANGLE:
The longest side is the HYPOTENUSE.
So, here H = 41
Now, by PYTHAGORAS THEOREM:


Hence, Pythagoras theorem for Right angled triangle is SATISFIED
So, error was CHOOSING the CORRECT hypotenuse in the given sides.
The correct H = 41 units and NOT 40 units.