for a firm with Cobb-Douglas production function
q = f (k, L) = k ^ (1/2) L ^ (1/2)
calculate the total, average and marginal cost.
q = k1/2L1/2
Total cost (C) = wL + rK
Total cost is minimized when MPL/MPk = w/r
MPL = q/L = (1/2) x (k/L)1/2
MPk = q/k = (1/2) x (L/k)1/2
MPL/MPk = k/L = w/r
wL = rK
Therefore,
L = rK/w
k = wL/r
Substituting in production function,
q = L1/2(wL/r)1/2 = L1/2L1/2(wL/r)1/2 = L x (w/r)1/2
L = q x (r/w)1/2
k = wL/r = (w/r) x q x (r/w)1/2 = q x (w/r)1/2
Substituting in total cost function,
C = wL + rK = w x q x (r/w)1/2 + r x q x (w/r)1/2 = q x (wr)1/2 + q x (wr)1/2 = 2q x (wr)1/2 [Total cost]
Average cost = C/q = 2 x (wr)1/2
Marginal cost = dC/dq = 2 x (wr)1/2
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