## Elements of geometry, based on Euclid, book i |

### From inside the book

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Page 7

... is that which has a

... is that which has a

**right**angle . 28. An obtuse - angled triangle is that which has an obtuse angle . 29. An acute - angled triangle is that which has three acute**angles**. 30. Of**four**- sided figures , a square is DEFINITIONS . Page 8

... angles

... angles

**right angles**. 34. Parallel straight lines are such as are in the same plane , and which being produced ever so far both ways do not meet . 35. A parallelogram is a**four**- sided figure of which the opposite sides are parallel ... Page 23

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...

**angles**shall be equal . Let the two straight lines AB , CD cut one another in the point E. The angle AEC shall be equal to angle DEB , and the angle CEB to the angle AED . A E B < CEA +**4**AED == 2**right**PROOF . Because the straight line ... Page 38

... angles BAC , ABC ( Ax . 2 ) . To each of these equals add the angle ACB . ACB Therefore the angles ACD , ACB are equal to the three angles CBA , BAC , ACB ( Ax . 2 ) . But the angles ACD , ACB are equal to two right ...

... angles BAC , ABC ( Ax . 2 ) . To each of these equals add the angle ACB . ACB Therefore the angles ACD , ACB are equal to the three angles CBA , BAC , ACB ( Ax . 2 ) . But the angles ACD , ACB are equal to two right ...

**four right angles**... Page 39

... right angles . The interior angle ABC , with its adjacent exterior angle ABD , is equal to two right angles ( I. 13 ) ...

... right angles . The interior angle ABC , with its adjacent exterior angle ABD , is equal to two right angles ( I. 13 ) ...

**four right angles**, are equal to twice as many right angles as the figure has sides ( I. 32 , Cor . 1 ) ...### Other editions - View all

### Common terms and phrases

ABC is equal adjacent angles alternate angles angle ABC angle BAC angle BCD angle contained angle EDF angle EGB angle GHD angles BGH angles CBE angles equal bisect centre cloth Const describe the circle diagonal equal sides equal to BC equal triangles equilateral triangle exterior angle Fcap four right angles GHD Ax given point given rectilineal angle given straight line given triangle gram HENRY EVERS interior and opposite isosceles triangle join less Let ABC LL.D meet opposite angles parallel straight lines parallel to BC parallelogram ABCD perpendicular Post 8vo PROOF PROOF.-Because Q. E. D. Proposition rectilineal figure remaining angle right angles Ax side BC sides are opposite sides equal square described square GB third angle trapezium triangle ABC triangle DEF WILLIAM COLLINS

### Popular passages

Page 23 - When a straight line standing on another straight line makes the adjacent angles equal to one another, each of the angles is called a right angle; and the straight line which stands on the other is called a perpendicular to it.

Page 33 - If two triangles have two angles of the one equal to two angles of the other, each to each ; and one side equal to one side, viz.

Page 43 - Parallelograms upon the same base, and between the same parallels, are equal to one another.

Page 15 - The angles at the base of an Isosceles triangle are equal to one another ; and if the equal sides be produced, the angles upon the other side of the base shall also be equal. Let ABC be an isosceles triangle, of which the side AB is equal to AC, and let the straight lines AB, AC...

Page 11 - Things which are double of the same, are equal to one another. 7. Things which are halves of the same, are equal to one another.

Page 37 - If a straight line meets two straight lines, so as to " make the two interior angles on the same side of it taken " together less than two right angles...

Page 41 - ... together with four right angles, are equal to twice as many right angles as the figure has sides.

Page 15 - J which the equal sides are opposite, shall be equal, each to each, viz. the angle ABC to the angle DEF, and the angle ACB to DFE.

Page 55 - IF the square described upon one of 'the sides of a triangle be equal to the squares described upon the other two sides of it ; the angle contained by these two sides is a right angle.

Page 24 - If, at a point in a straight line, two other straight lines, on the opposite sides of it, make the adjacent angles together equal to two right angles, these two straight lines shall be in one and the same straight line.