Answer: x=15.6
Explanation:
An isosceles triangle has two congruent sides. (1 pair). So, the other side (not x) must equal 11.
Using the Pythagorean Theorem; a^2+b^2=c^2, you can substitute the values in as follows
11^1+11^2=x^2
121+121=x^2
242=x^2
15.55634918610405=x
round to the nearest tenth as said in the question...
x=15.6