12 求 微 分 方 程 式 y′′ + 0.5 y′ − 0.5 y = e x + sin(x) + 3 cos(x), y(0) = 0, y′(0) = 1.5 之 解 , 其 中 : (A) y = e x /2 + e x − 2 cos(x) (B) y = 3e x/ 2 − 3 cos(x) (C) y = e− x cos(x) − 1 (D) y = e x/ 2 − e x + 2 sin(x)
5.Assuming the magnetic field in the magnetotail is time-independent and only has the x component
varying with 2, as shown below. The electric field is uniform and time-independent.
【題組】(c) Discuss your answer in (a) with the direction of cross tail current. (8 points)