Shade the region of the xy-plane for which
a) (𝑥2+𝑦2−16)(𝑥2−4)≤0
b) (𝑦−𝑥)(𝑦2+𝑥3)>0
Before shading this region, let's study geometrically to which region it corres[onds. The first inequality is achieved, when two expressions () have opposite signs. Now there is two cases : , in this case the point should be in the circle centered at 0 of radius 4 (due to the first inequality) and it should have due to the second case. The second case is when the point is outside the circle centered at 0 of radius 4, but it has . Thus we obtain a region like this :
We will study this region similarly to the previous one : this expression is positive if both the epressions are of the same sign. There is two cases: or . The first case corresponds to points that are higher than the straight line , and for the points we have additional condition . In the other case we have points that are lower than , we can't have points (as we can't have ) and for we have an additional condition . Thus we obtain a region like this :
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