《注意题中条件》mx+ny的最大值为(ab)~(1/2).提示:错解中等号成立的条件是a=b,而已知条件中a≠b,故取不到最大值1/2(a+b).可借助三角代换求解.《求电流大小的范围》把R_3分成R和R_3-R两部分,将图1化简成图2,外电路的结构是R与R_2串联,(R_3-R)与R_1串联,然后这两串电阻并联.设外电路电阻为R′,由串、并联电路 Note that the maximum value of condition mx + ny is (ab) ~ (1/2). Hint: The condition that the misalignment medium number is established is a = b, while the known condition a ≠ b, so the maximum The value of 1/2 (a + b) .Can be solved by means of the triangle. “Find the current size of the range” The R_3 is divided into two parts R and R_3-R, Figure 1 simplified into Figure 2, the external circuit structure is R And R_2 in series, (R_3-R) and R_1 in series, and then the two series resistance in parallel set the external circuit resistance R ’, by the series and parallel circuit