You setup the equation right, but your algebra is incorrect.

162 / n = n / 18 162 = n^2 / 18 (this is where you went wrong) 162 * 18 = n^2 2916 = n^2 54 = n

You should be able to work out the rest for yourself.

RickyOswaldIOW

2006-03-30 02:59:45

ux / u(x-1) = ratio

Is this correct?

RickyOswaldIOW

2006-03-26 00:25:58

Thanks Ganesh. Will have to study this a bit more

ganesh

2006-03-25 16:37:20

In a GP, u3 = 18 and u5 = 162. Find u1.

rickyoswaldiow, u3*n=u4, u3*n²=u5 That is, n²=u5/u3=162/18=9, n=3. u1*n²=u3. Therefore, u1*9=18, u1=2. The Geometric Progression is 2, 6, 18, 54, 162, 486..... The first term is 2 and the common ratio is 3.

RickyOswaldIOW

2006-03-25 16:10:33

162 = n² / 18n

Is this along the right track?

RickyOswaldIOW

2006-03-25 16:08:10

In a GP, u3 = 18 and u5 = 162. Find u1.

I know that in a GP, ux / u(x-1) = ratio (r). I deduce from that;

u5 / n == n / u3.

so 162 / n = n / 18

I then try to balance this - I think that's where I am going wrong.

162 = 2n/18 2916 = 36n n = 81 Which is of course incorrect. Where am I going wrong?