[填空题]
Consider the function fed*u5kt*dceoqe :e 55 5v j.wf5jzl ;x ;kqz *iqw;4pr3,pnqz defined by $ f(x)=\ln \left(4 x^{2}-9\right) $ for $x>\frac{3}{2}$ . The following diagram shows part of the graph of f which crosses the x -axis at point A , with coordinates (a, 0) . The line L is the tangent to the graph of f at the point B .
1. Find the exact value of a .
2. Given that the gradient of L is $\frac{1}{2}$ , find the x -coordinate of B .
