Answer:
16.7
Step-by-step explanation:
In a right triangle, a²+b²=c², with c representing the hypotenuse. In a right triangle, the hypotenuse is the side opposite of the right angle, or the angle symbolized by the square. Here, the right angle is opposite of the side with a length of 20, so we can say that
c = 20
Therefore,
a²+b² = 20², with a and b representing the other two sides*. Because 11 is given as another side, we can say
11² + b² = 20²
121 + b² = 400
subtract 121 from both sides
279 = b²
square root both sides
b = √279 ≈ 16.7 as the third side
* for our purposes, it does not matter which side is a and which side is b
