The author posted a question in Education
descriptive geometry can't understand the principle? and got a better answer
Response from
Response from 0[++++]
<img src=https://otvet.imgsmail.ru/download/27615052_4a63e6fa7228536f52f246ebd5c4357b_800.jpg data-lsrc=//otvet.imgsmail.ru/download/27615052_4a63e6fa7228536f52f246ebd5c4357b_120x120.jpg data-big=1>
<img src=https://otvet.imgsmail.ru/download/27615052_4a63e6fa7228536f52f246ebd5c4357b_800.jpg data-lsrc=//otvet.imgsmail.ru/download/27615052_4a63e6fa7228536f52f246ebd5c4357b_120x120.jpg data-big=1>