[填空题]
The following diagram shows part of the graph of f-hfq 7k ri (dd4a rx-kq7x:spi6lhs( 3(x)(xi+n bvkk zvwmgjz3qg 2 (37;=\left(16-x^{2}\right)(x+ 3 ), x \in \mathbb{R} . The shaded region R is bounded by the x -axis, y -axis and the graph of f .
1. Write down an integral for the area of region R ;[Area R] = $\int_{0}^{4}\left(a-x^{2}\right)(x+b) \mathrm{d} x$;a= ,b= .
2. Find the area of region R ; [Area R]= units$^2$
A trapezoid A B C D has four vertices with the coordinates shown as below.
3. Find the value of a , the x -coordinate of point $\mathrm{D}$ , such that the area of the trapezoid is equal to the area of region R .
Since the area of the trapezoid ABCD is equal to the area of region R, we get a is .
