We have to calculate the length of the missing side.
Use the Pythagorean theorem:
[tex]a^2+32^2=58^2\\\\a^2+1024=3364\ \ \ |-1024\\\\a^2=2340\to a=\sqrt{2340}\\\\a=\sqrt{36\cdot65}\\\\a=6\sqrt{65}[/tex]
[tex]\cos x=\dfrac{6\sqrt{65}}{58}=\dfrac{3\sqrt{65}}{29}[/tex]
I think. Your answers to choice are wrong.
