Books Books
... the three angles of a triangle are together equal to two right angles, although it is not known to all.
The Works of John Playfair ...: With a Memoir of the Author ... - Page 335
by John Playfair - 1822

## Iron: An Illustrated Weekly Journal for Iron and Steel ..., Volume 15

Perry Fairfax Nursey - 1831 - 508 pages
...has been before proved that the angle ADe is an acute angle of 90 degrees, whence it follows that as the three angles of a triangle are together equal to two right angles, the remaining angle /AD must likewise be an acute angle of 90 degrees, and, as before, since the two angles/...

## Encyclopædia Americana: A Popular Dictionary of Arts, Sciences ..., Volume 10

Francis Lieber, Edward Wigglesworth - 1832 - 656 pages
...numbers. Of tho geometrical theorems which are ascribed to him, the following are the most important : The three angles of a triangle are together equal to two right angles ; and in aright-angled triangle, the square of the hypothenuse is equal to the sum of the squares of...

## Encyclopaedia Americana: A Popular Dictionary of Arts, Sciences ..., Volume 10

Francis Lieber, Edward Wigglesworth, Thomas Gamaliel Bradford - 1832 - 708 pages
...numhcfs. Of tho geometrical theorems which are ascribed to him, the following are the most important : The three angles of a triangle are together equal to two right angles ; and in a right-angled triangle, the square of the hypothenuse is equal to the sum of the squares...

## Letters of Euler on Different Subjects in Natural Philosophy ..., Volume 2

Leonhard Euler, Sir David Brewster - 1833 - 446 pages
...impossible to draw any conclusion with respect to real objects; thus, when I have demonstrated that the three angles of a triangle are together equal to two right angles, this is a property belonging only to an abstract triangle, and not at all to one really existing. You...

## Letters of Euler on Different Subjects in Natural Philosophy ..., Volume 2

Leonhard Euler, Sir David Brewster - 1833 - 442 pages
...impossible to draw any conclusion with respect to real objects ; thus, when I have demonstrated that the three angles of a triangle are together equal to two right angles, this is a property belonging only to an abstract triangle, and not at all to one really existing. 32...

## The Gallery of Portraits: with Memoirs ...

1833 - 504 pages
...advanced as far as the thirty-second proposition of the first book of Euclid. He had perceived that the three angles of a triangle are together equal to two right ones, and was searching for a satisfactory proof, when his father surprised him in his forbidden speculations....

## Library of Useful Knowledge: Geometry plane, solid, and spherical [by Pierce ...

1835 - 684 pages
...notwithstanding, of opinion, that the grand truth with which it is so intimately connected, viz., that " the three angles of a triangle are together equal to two right angles," may be referred to the general principle of Homogeneity. Of this it is unnecessary to say more in this...

## Prize Essay and Lectures, Delivered Before the American Institute ..., Volume 6

American Institute of Instruction - 1836 - 328 pages
...for a thousand years, furnishes no absolute assurance that it will rise tomorrow. But the truth that the three angles of a triangle are together equal to two right angles, is made as certain by a single demonstration, as it could be by a thousand. Apply now this illustration...