Hello from MrBillDoesMath!
Answer:
The length of the remaining side is sqrt (105.79). (Approximately 10.29 )
Discussion:
This is a right triangle (meaning it has a 90 degree angle) so the Pythagorean theorem applies. This states that
a^2 + b^2 = c^2
where "a" and "b" are the sides of the triangle and "c" is the hypotenuse (longest side). Suppose we call the side in the diagram without a length "a". Then by Pythagoras
a^2 + (3.9)^2 = 11^ 2 =>
a^2 + 15.21 = 121 => subtract 15.21 from both sides
a^2 = 121 - 15.21 = 105.79 => take the square root of both sides
a = sqrt (105.79) which is approximately 10.29
Thank you,
MrB