Prove that the value of the expersion y^2-10y+30 can only be a positive number PLEASE ANSWER ASAP WILL GIVE BRAINLIEST

Answer this question only if you know the 30 points and

Determine whether the following statements are true and give an explanation or counterexample. bold a. when using the shell method, the axis of the cylindrical shells is parallel to the axis of revolution. bold b. if a region is revolved about the y-axis, then the shell method must be used. bold c. if a region is revolved about the x-axis, then in principle it is possible to use the disk/washer method and integrate with respect to x or the shell method and integrate with respect to y.

Find the solution of this system of equation -7x+y=-20 9x-3y=36