[填空题]
The equation of a curve y3 f)p ub1wlv7is : uhar.i::( bet jz2fx y=-$x^{2}+8 x-12$ . A section of the curve is shown on the diagram below, with the two x -intercepts labelled.
1. Find $\frac{\mathrm{d} y}{\mathrm{~d} x}$ = -ax + b; a= ,b= .
2. Write down the coordinates of the local maximum, the local maximum is located at ( , )
3. Write down an integral representing the area of the shaded region.
4. Find the area of the shaded region.
A=$\frac{a}{b}$ units$^2$;a= ,b= .
