Applications of Integrals Review

Using the areas of each region given
$$\int_b^df\left(x\right)=$$  

Find the enclosed area by the curve with equation  $$y=4-x^2$$  ,the X-axis and the lines x = -1 and x = 2 

If   $$\int_{-5}^3g\left(x\right)dx=-2\$$   and  $$\int_{-5}^{15}g\left(x\right)dx=9$$   

Find the value of  $$\int_{15}^3\ \ g\left(x\right)dx$$  

Find the enclose area by the curve with equation $$f\left(x\right)\ =\ 2-x^2\$$  and  $$g\left(x\right)=-x$$  

The area under the curve y = sinx over the interval $$\left[0,\frac{\pi}{2}\right]$$

Find the average value of $$f\left(x\right)=\sqrt{2x-1}$$  

from  $$x=\frac{1}{2}$$  to  $$x=1$$  

 Find the area under  $$y=\left(x-2\right)^5$$   over the interval $$\left[2,4\right]$$

1.What should "u" equal in this integral?