difficult / hard, probably impossible

(geometry) an orthocenter

to find / to seek, to look for / to desire, to wish / to demand, to sue, to compel

question, problem on homework etc. / a question; a matter (of time etc.) / a problem (something that needs to be dealt with); a trouble / an issue; a matter

obtain the ratio

a triangle (polygon)

(informal) no problem

unthinkable, out of the question

practical question (problem)

matter of life or death / (idiomatic) an extremely urgent matter