# geometry

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1. sum of interior angles
(n-2)180
2. number of diagonals of any polygon is:
n(n-3)/2
3. pythagorean theorem
a2 + b2 = c2
4. special right triangles
• 3-4-5
• 6-8-10
• 12-16-20
• 5-20-25
• 5-12-13
• 10-24-26
• 8-15-17
• 7-24-25
5. the presence of long legs in a right triangle signifies that...
the missing side should be determined by the means of x2 - y2 = (x+y)(x-y)
6. special right triangle 45-45-90
the legs have ratio
x:x:x(sq root)
7. If the legs of a right triangle are equal
the triangle is necessarily a 45-45-90
8. 30-60-90 triangle has angles
x: x( cubed root): 2x
9. if the length of the hypotenuse of a right triangle doubles the length of one of its legs...
it is a 30-60-90
10. how many 30-60-90 triangles are in a hexgon?
twelve
11. in similar triangles the ratio of the areas of two similar triangles is equal to...
the square of the ratio of the corresponding sides
12. area of a triangle
1/2 * base * height
13. area of rectangle and square
length * width
14. area of parallelogram or rhombus
base times height
15. area of a rhombus as well is...
diagonal 1 * diagonal 2/ 2
16. area of a trapezoid
base 1 * base 2 / 2 * height
17. area of a circle
pie * r2
18. circumference of a circle
2pie *r
19. circumference of a circle
2 * pie * r or pie * d

pie = 22/7
20. length of an arc
2 * pie * r * x/360
21. length of a sector of a circle
pie * r2 * x/ 360
22. Inscribed angle properties
• 1. the inscribed angle of an arc is always half the measure of its central angle
• 2. inscribed angles drawn to the same arc have equal measures.
• 3. the inscribed angles of equal measure have arcs of equal length and arcs of equal length have inscribed angles of equal measure.
23. inscribed and circumscribed polygons
• 1. an inscribed or circumscribed polygon always has the same center as the circle.
• 2. is a triangle is inscribed in a circle so that one of its sides is the diameter of the circle then that triangle is always a right triangle.
24. volume of rectangular solid
length * wideth * height
25. surface area of rectangular solid
2 (lw +wh+ hl) or sum of the area of its faces.
26. diagonal of rectangular solid...
square root of l2 + w2 + h2
27. volume of a cube
28. volume of a cube
s3
29. surface area of a cube
30. 6s3
31. diagonal of a cube
s square root of 3
32. volume of a cylinder
pie *r2 * height
33. surface area of a cylinder
2 * pie * r * h + 2 (pie * r2)
 Author: kaytea1112 ID: 28708 Card Set: geometry Updated: 2010-08-02 12:40:09 Tags: gre math geometry Folders: Description: arrrr Show Answers: