15 m is the answer.
Length of one leg = 20 m
Length of the hypotenuse= 25m
As it is a right angled triangle we can use pythogoras theorem.
Let the unknown length be y
(20) (20) + y(y) = (25) (25)
400 + y(y) = 625
y(y) = 225
y = √225
y = 15
The length of the unknown leg is 15 m.
What is Pythagorean theorem?
A theorem states that the square of the length of the hypotenuse of a right triangle is equal to the sum of the squares of the lengths of the other sides. It is mathematically stated as c2 = a2 + b2 , where c is the length of the hypotenuse and a and b are the lengths of the other two sides.
Pythagoras theorem can be used to find the unknown side of a right-angled triangle. For example, if two legs of a right-angled triangle are given as 4 units and 6 units, then the hypotenuse (the third side) can be calculated using the formula, c2 = a2 + b2; where 'c' is the hypotenuse and 'a' and 'b' are the two legs.
Learn more about right triangle here:https://brainly.com/question/2217700
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