# quasi concavity/quasi convexity. Classic List Threaded 9 messages Open this post in threaded view
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## quasi concavity/quasi convexity.

 Consider the production function: Q = max {K, L} Which of the following is true about Q? a) Q is both quasi-convex and quasi-concave b) Q is quasi-convex and not quasi-concave c) Q is quasi-concave and not quasi-convex d) Q is neither quasi-convex nor quasi-concave
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## Re: quasi concavity/quasi convexity.

 Q is only quasiconvex because its lower contour/level set is a convex set.
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## Re: quasi concavity/quasi convexity.

 isn't the upper contour set also convex, since the funcction is a cube. Also Q=max{k,l} is a concave function and aren't concave functions quasi concave too?
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## Re: quasi concavity/quasi convexity.

 In reply to this post by Dreyfus I think its both quasi concave and quasi concave.
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## Re: quasi concavity/quasi convexity.

 But the answer is option b. I don't know how.
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## Re: quasi concavity/quasi convexity.

 In reply to this post by lucy Hi Lucy, just plot the level curves for this function with some constant c = max{L,K}. On plotting you will find that the level curves are mirror image of inverse L shaped curves and the convex set is the lower level set not the upper level set. And also Since L and K are linear functions thus they are both convex and concave functions but Q(L,K)=max(L,K) is a "Convex function" not "Concave function"!
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## Re: quasi concavity/quasi convexity.

 Isn't the max function concave?? 