# GRE_Math_.txt

 Area of a triangle 1/2 (base)(height) Special Right Traingles 3-4-5 (or any multiple of); right triangle; given any 2-find 3rd side length30-60-90; side ratio of X:Xsqrt(3):2X5-12-13 (or any multiple of); right triangle;given any 2-find 3rd side length45-45-90; side ratio of X:X:Xsqrt(2) Circumference of a circle 2(pi)r Arclength If n is a degree measure- S= 1(n/360)(2pi(r))S=(ratio of degree part:whole)(circumference) Area of a circle (pi)r^2 Area of a circular sector If n is the degree measue of the sector's central angle- A= 1(n/360)(pi(r^2))A=(ratio of degree of sector:degree of circle)(area of circle) Interior Angles of a polygon The sum of the interior angles of a polygon= (n-2)(180), where n is the number of sides Surface area of a rectangular solid 2lw+2wh+2lh Volume of a rectangular solid solid =lwhcube =(=l^3) Volume of a cylinder (pi)(r^2)(h) Percent formula Part= (perecnt)(whole) Probability Favorable/Possible Solving an inequality When multiplying or dividing both sides by a negative number you must reverse the sign Midpoint between (x1, y1), (x2, y2) = [(x1+x2)/2], [(y1+y2)/2] Divisible by 2 If last digit is divisible by 2 Divisible by 3 If the SUM of its digits is divisible by 3 Divisible by 4 If last two digits are divisble by 4 Divisible by 5 Ends in 0 or 5 Divisible by 6 If it is divisible by both 2 (last two digists divisible by 2) and 3 (SUM of its digits is divisble by 3) Divisible by 9 If the SUM of its digits is divisible by 9 First 25 primes (<100) 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97 complimentary lines make up a right angle supplementary lines make up a straight line Ratio of areas of two similar triangles square of the ratio of corresponding lengths (if triangle b is twice the size of triangle a, (2/1)^2=4; 4 times the area of triangle a) Special right traingle side length ratios 1:1:(sqrt)2 -isosceles right triangles 1:(sqrt)3:2 -30-60-90 triangle pythagorean triplets 3,4,5 (and any multiple of these e.g., 6,8,10) 5,12,13 (and any multiple of these) Surface area of a cylinder A=(circumfrence of circular base)(height)+(2area of circular bases)A=[(2pi(r)h)] + [2(pi)r^2)] The diagonal through a box d^2=(l^2)+(w^2)+(h^2) Area of a trapeziod 1/2(b1+b2)(h) Counting Principle -two tsks; N ways to do/choices for the first and M was to do/choices for the second (NM)Use anytime a question asks, "how many" (ways to do..., numbers between..., arrangments of...) Probability an experiment will replicate (probability of first event)(probability of second)(...)...[ex; coin landing heads 3x in a row; (1/2)(1/2)(1/2)=1/8] Probability of E and F occurring Independent: p(E and F) = p(E) x p(F)Dependent: p(E and F) = p(E) x p(FlE)Conditional: p(FlE) = p(E and F)/p(E)0 if mutually exclusive Probability of E or F occurring p(E)+p(F) - p(E and F) If mutually exclusive: p(E)+p(F) Common factorials 0!=11!=12!=23!=64!=245!=1206!=5040 Permutation (without replacement) (nPr) (ways to select officers) The number of ways of obtaining an ordered subset of elements from a set of elements is given bynPr=n!/(n-r)! Permutation (with replacement) (nPr) "permutation lock" n^r Combination (without order) (nCr) Number of combinations of n distict objects taken r at a timen!/[r!(n-r)!] = nPr/r! Authorghstechnology ID82464 Card SetGRE_Math_.txt Descriptionmath Updated2011-04-28T12:34:28Z Show Answers