經濟學有q function and p 如何求MR??

Given demand function Q = 600 - 100P
Marginal revenue function must be Q = 300 - 50(MR)

On the graph, the slope of MR is twice that of the demand curve, or MR is falling twice as fast as P.

Why? When demand elasticity = 1, i.e., at the mid-point of the demand curve, MR = 0. At unitary elasticity, change in price does not change total revenue, therefore MR must be 0. MR must bisect the horizontal axis of the demand curve.


圖片參考：http://f20.yahoofs.com/hkblog/1o4zXniVEQVTy_tSMhfH__DOT__tHZ_1/blog/ap_20090115060453955.jpg.jpg?ib_____Dr223JFD5

From the demand function Q = 600 - 100P
P = 4, Q = 200

Substitute Q into the MR function
200 = 300 - 50(MR)
MR = 2