Answer:
X = 18
Step-by-step explanation
The shown figure of isosceles triangle can be drawn as :
Now it become a right angle triangle
From right angle triangle rule
hypotenuse² = Perpendicular² + Base²
i.e 15² = 12² + (

or 15² - 12² =

or 225 - 144 =

or 81×4 = x²
or x=

i.e X= 18 Answer