Abstract: In electromagnetism teaching, the resonance circuit is usually solved by using vector diagram or complex number method, which demands the knowledge of rotating vector or complex representation for oscillations, respectively. A direct method is introduced in this paper, i.e., the solution is obtained by straightforward calculation of oscillation functions (trigonometric functions). The method can be extended to general alternative current circuit. The method demands less preliminary knowledge, and may be suitable for the course of “College Physics” for majors other than physics. 

Key words: alternating-current circuit, resonance, trigonometric function