Предмет: Геометрия, автор: isparygin

Площадь поверхности куба равна 722. Найдите его диагональ. Полное решение.

Ответы

Автор ответа: Fortun

Диагональ куба вычисляется по формуле $d ^{2} = 3a ^{2}$ , где d - диагональ, а а - сторона куба.
При этом $a^{2}$ - это площадь поверхности одного квадрата, являющегося одной из шести сторон куба.
Получается, что квадрат диагонали равен площади трёх сторон куба, значит удвоенный квадрат диагонали = пощади шести сторон, то есть всей поверхности куба.
$2*d ^{2} = 2*3a^{2} = 722$
$d ^{2} = 361$
d = 19

isparygin: Благодарю.

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The Open University
A university that calls itself 'The Open University' suggests (предполагает) that all other universities are closed. And this is true, because they are closed to everyone who does not have the time, the opportunity (возможности) or the qualifications to study there. For these people, who missed (упустить) the chance of going to a conventional university, 'The Open University' was set up in 1967.
Most of its students work at home or in full-time jobs and can study only in their free time. They need to study about ten hours a week. As the university is truly "open", there are no formal entry requirements (вступительных экзаменов) (none of the usual "A" Level examinations are asked for), and students are accepted (приниматься) on a "first come, first served" basis. This is one of the more revolutionary aspects of the university.
Its students are therefore of all ages and come from very different backgrounds (происхождение). Some, such as teachers, want to improve (улучшить) their qualifications. Others, like retired people (пенсионеры) or mothers whose families have grown up, are at the O. U. because they now have the time to do something they have always wanted to do.
Returning to "school" is difficult for most students, for they have forgotten — or never knew — how to study, to write essays, and to prepare for exams. In addition to all the reading and writing assignments (задание), students have got a lot of watching and listening to do, for there are weekly O. U. lectures broadcast on BBC television and radio.
To keep people from just giving up or collapsing under all this work, each student gets the help and support of his own tutor/counselor, who he meets regularly and can telephone in any crisis or difficulty. At the meetings, students get to know other students on the course and join (объединяться) with them into "self-help" groups. These groups meet in each others homes to discuss the texts and assignments; here too they find support and stimulation.
By the time the exams come in October, you feel much more confident (уверенный) and optimistic about your return to student life. Your final mark is based on the exam and the written assignments done during the year.