The equation of the curve is $\displaystyle y=8x-x^2$

Q)Find the coordinates of the stationary point of the curve.

I know that I am supposed to express this equation in the form $\displaystyle a-(x+b)^2$ and then get the values of b for x and a for y to get the answer. But what are stationary points? Is that the vertex?

Q)Find the set of values ofxfor whichyisgreater than equal to -20

I've got the final answer

(x+2)(x-10)isless than or equal to 0

x= -2 or x= 10

Now what I don't understand is what is the sketch method? And how to easily find out which of the two (-2 or 10) is less than or equal to x or which one is greater than or equal to x.

Thanks a lot in advance.