x is equal to 58 degrees.
In order to find this, we first need to note that the cos function is equal to the adjacent side divided by the hypotenuse. This allows us to see the following equation.
Cos(Angle) = Adj/Hyp
Now we can input the parts that we know.
Cos(x) = 9/17
Cos(x) = 0.529411765
To undo this cos function and find the angle, we need to use the arccos function. Using the arccos function undoes a cos similar to how division undoes multiplication.
x = Arccos(0.529411765)
x = 58 degrees