CHAPTER 19 KEY FORMULAS AND EQUATIONS

Arithmetic sequences

Recursion formula
an = an − 1 + d(19.1)
nth term
an = a1 + (n − 1)d(19.2)
Sum of n terms
Sn = n2(a1 + an)(19.3)

Geometric sequences

Recursion formula
an = ran − 1(19.4)
nth term
an = a1rn − 1(19.5)
Sum of n terms
Sn = a1(1 − rn)1 − r(r ≠ 1)(19.6)
Sum of an infinite geometric series
S = a11 − r(| r|  < 1)(19.7)
Factorial notation
n !  = n(n − 1)(n − 2) ⋯ (2)(1)(19.8)
Binomial formula
(a + b)n = an + nan − 1b + n(n − 1)2 !  an − 2b2 + n(n − 1)(n − 2)3 !  an − 3b3 +  ⋯  + bn(19.9)
Binomial series
(1 + x)n = 1 + nx + n(n − 1)2 !  x2 + n(n − 1)(n − 2)3 !  x3 +  ⋯ (19.10)

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