x is equal to 12.
First we find the value of the triangle that has the values of the hypotenuse and either side of the right angle triangle by using the Pythagoras theorem.
a^2 + 8^2 = 17^2.
a^2 = 289 - 64
a = /225
a = 15
Then we find the value of x by subbing the value of a, which is 15 and use the Pythagoras theorem again.
x^2 + 9^2 = 15^2
x^2 = 225 - 81
x = /144
x = 12