Thanks for your response. Given your clarification (alternately, perhaps I misunderstood your original post) I retract my criticism. If you drew a picture and

Thanks for your response. Given your clarification (alternately, perhaps I misunderstood your original post) I retract my criticism. If you drew a picture and engaged, and he actively wanted a closed form and didn't want to see you work it out slowly, then that's a poor interviewer, not on you at all! I will note that I do occasionally ask "do you happen to know if there's a closed form" for things, as an extra credit kind of thing, making clear I'm curious and I don't expect a yes. Someone could easily get the impression this is a high stakes question if I wasn't clear it's not; conceivably that was the intent in this situation. But any which way, sounds frustrating and the interviewer was either a jerk or unclear.