tangent line at what point on the curve?
"area limited by the curve" limited by what?
one horizontal tangent line is at
another horizontal tangent line, , touches the curve at two points ...
here lies the dilemma ...
the horizontal tangent line (the x-axis) bounds the curve above. there are two symmetrical regions formed by the curve below the x-axis.
second possible region ...
the horizontal line bounds the curve below ...
I recommend that you graph the original function on a calculator so you can visualize what I'm talking about.