Question

The first and last term of G.P. are a and l respectively; r being its common ratio; then the number of terms in this G.P. is-
a.(​log l - log a)/log r
​b.l - (log l - log a)/log r
c.(log a - log l)/log r
​d.l + (log l - log a)/log r

Answer 1

Answer:

(d)

Step-by-step explanation:

The n-th term is:   a r^(n-1).

Given:

n-th term is l

=> a r^(n-1) = l

=> r^(n-1) = l/a

=> (n-1) log r = log l - log a

=> n - 1 = ( log l - log a ) / log r

=> n = 1 + ( log l - log a ) / log r           ... and that is option (d)

Answer 2

Answer

Step-by-step explanation: