Question

For a G.P if t4=16 and t9= 512 find s10

Answer 1

Answer:

T4=ar^3=16......(1)

T9=ar^8=512......(2)

equating (1) and (2)

16/r^3=512/r^8

r^5=512/16

r^5=32

r^5=(2)^5

therefore, r=2......(3)

and a=16/(2)^3

therefore , a=16/8=2....(4)

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

S10=a(1-(2)^10)/(1-2).......(from 3)

=2(1-1024)/(-1)......(from 4)

=2(1023)

=2046

hope it helps......

Answer 2

Answer:

Step-by-step explanation:

t4= ar^3=16...(1)

t9=ar^8=512...(2)

Dividing (1)and(2)

t9\t4 =512\16

r=2

Putting r=2 in (1)

16=ar^3

16=a*2*2*2

a=2

So therefore,

S10=a*(1-r^10)\(1-r)

=2*(1-2^10)\(1-2)

=2047

Hope it helps!