Question

For a GP if t3=18. T6=486 find S5

Answer 1

Given,In a GP t3=18 and t6=486

To find : S5

We know that

tn=a*r^(n-1)

So,t3=a*r^2=18                    .................Eq.(1)

Also, t6=a*r^5=486

=>t6=a*r^2*r^3=486            .................Eq.(2)

Substituiting Eq.(1) into Eq.(2)

We get, 18*r^3=486

=> r^3=27

So, r=3

Subtituiiting the value of r into Eq.(1)

=>a(3)^2=18

=>a=2

We know that

Sn=a(1-r^n)/1-r

=>S5=2(1-(3)^4)/1-3

=>S5=2(-242)/-2

=>S5=242.

Thanks!!!

Answer 2

Answer:

hope it will help you

S5=242