ANSWER
C. 9
EXPLANATION
We use the Altitude Theorem,to find the value of a.
According to the altitude theorem, the height of the triangle of the triangle is equal to the geometric mean of the two segment it creates on the hypotenuse.
[tex]6 = \sqrt{4a} [/tex]
Square both sides to get,
[tex]36 = 4a[/tex]
[tex]9 = a[/tex]
The correct choice is option C.
