Question

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

Answer 1

Answer:

given that

a (first term) = 5

d (common difference ) = 15

11th term we need to find so

n 11 = a + (n-1) x d

     = 5+ (11-1) x 15

    = 5 + 10 x 15

    = 5 x 150

   = 155

   

Answer 2

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

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