1.

Find the 11th term of the geometric sequence 5, 20, 80, ...

Answer»

GIVEN :

  • First TERM (a) = 5
  • Common RATIO (r) = 20/5 = 4

To FinD :

  • 11th term of sequence

SolutioN :

Use FORMULA for last term of GP

\dashrightarrow \boxed{\tt{a_n \: = \: ar^{n \: - \: 1}}} \\ \\ \footnotesize \underline{\sf{\: \: \: \: \: \: Put \: n \: = \: 11 \: \: \: \: \: \:}} \\ \\ \dashrightarrow \tt{a_{11} \: = \: 5 \: \times \: 4^{11 \: - \: 1}} \\ \\ \dashrightarrow \tt{a_{11} \: = \: 5 \: \times \: 4^{10}} \\ \\ \dashrightarrow \tt{a_{11} \: = \: 5 \: \times \: 1,048,576} \\ \\ \dashrightarrow \tt{a_{11} \: = \: 5,242,880} \\ \\ \underline{\sf{\therefore \: 11th \: term \: of \: GP \: is \: 5,242,880}}


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