Yòng sānjiǎo chǐ kěyǐ huà chū jīngzhǔn de zhíjiǎo.
You can draw a precise right angle with a set square.
Tips
memory
直 means 'straight/upright' and 角 means 'angle/corner.' A right angle is literally a 'straight corner' — the angle where two lines meet perfectly upright.
