Math Formulas + Facts

Sum of cubes and Difference of Cubes
a3 + b3 = (a + b) (a2 − a b + b2 )
a3 - b3 = (a - b) (a2 + a b + b2 )

 Powers to know
57 = 78125
56 = 15625
55 = 3125

 Compound Interest
A = P(1+r/n)nt

 Harmonic Series

 1+1/2+1/3+1/4+1/5+1/6...+1/n

 To estimate sum, take the 20 term for 1, then take the next 21 terms for 2, then take the next 22 terms for 3....

 Sums:
2 - up to 1/4
2.5 - up to 1/7
3 - up to 1/11
3.5 - up to 1/19
4 - up to 1/31
4.5 - up to 1/51
5 - up to 1/83

 Area of Octogon
A = 2(1+√2)a2

 Finding the number sides of a regular polygon when you know the interior angle in degrees
180-x° = 360/n

 Finding total number of diagonals in a polygon
n(n-3)/2

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