Step-by-step explanation:
it is a right-angled triangle, so the side lengths need to fulfill the Pythagoras rule :
c² = a² + b²
where c is the Hypotenuse, the baseline opposite of the 90 degree angle. and a and b (often called legs) are the sides "enclosing" the 90 degree angle.
so, we have
20² = a² + 12²
400 = a² + 144
a² = 256
a = 16
FYI - we could have picked the right answer also by eliminating the wrong given answer options.
as this is a right-angled triangle :
a cannot be longer than the baseline (20).
that eliminates already the first 2 options.
and then look at the picture : a cannot be shorter than b (the other side line (12)).
that eliminates the third option.
