consider the first technique. If this is used, then we need to have 2x1 +x2 = q. Since this is linear, the firm will typically specialize and set x2 = q or x1 = q/2 depending on which is cheaper. Hence the cost function for this technique is q = min{w1/2,w2}. Similarly, the cost function for the other technique is q = min{w3,w4/2}. Since both techniques must be used to produce q units of output,
c(w1,w2,w3,w4,q) = q[min{w1/2,w2} + min{w3,w4/2}]
x1 =q/2 if w1/2 < w2 =∈ [0,q/2] if w1/2 = w2 =0 if w1/2 > w2
x2 =0 if w1/2 < w2 , =∈ [0,q] if w1/2 = w2 =q if w1/2 > w2