Difference between revisions of "Math for CS Review"

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(Memorize)
(Memorize)
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* ''Formulae''
 
* ''Formulae''
 
** Arithmetic Sum: (1 + 2 + ... + n) = n * (n+1) / 2
 
** Arithmetic Sum: (1 + 2 + ... + n) = n * (n+1) / 2
** Geometric Sum: 1 + r + r<sup>2</sup> + r<sup>3</sup> + ... + r<sup>n</sup> = (r<sup>n+1)-1) / (r-1)
+
** Geometric Sum: 1 + r + r<sup>2</sup> + r<sup>3</sup> + ... + r<sup>n</sup> = (r<sup>n+1</sup>-1) / (r-1)

Revision as of 19:04, 6 January 2020

Memorize

These are things you need to memorize.

  • Order of operations: first parenthesis, then exponents, then multiplication/division/modulus, then addition and subtraction. And left to right.
  • Powers/exponents
    • 210 = 1024, roughly 1 thousand
    • 2a+b = 2a * 2b
    • ya+b = ya * yb
    • 2-a = 1 / (2a)
    • 220 = 1024 × 1024, roughly 1 million
    • 230 = 1024 × 1024 × 1024, roughly 1 billion
  • Logarithms
    • logbx = y, means by = x, for any b > 1
    • log101000 = 3
    • log21024 = 10
    • logbx = logcx / logcb, for any b > 1, c > 1
    • log210 is about 3.32
    • logb(xy) = y logb x, for any b > 1
  • Formulae
    • Arithmetic Sum: (1 + 2 + ... + n) = n * (n+1) / 2
    • Geometric Sum: 1 + r + r2 + r3 + ... + rn = (rn+1-1) / (r-1)