3 replies to this topic

[Max018]

Hi all,

Just stumbled accross this site so a quick hi to all here! Anyway on with my question if I may!

Higher Maths - 2000 - Paper One - Question 5. I'd type it out but I cant find some of the characters for the recurrance relation formula!

I was thinking simultaneous equations but I'm confuzzled and the answers just dont help at all. lol.

Anyway thanks anyone for any help!
Paolo

[AndyW]

For the first, L = b / (1-a) = 10 / (1 - a)

For the second, L = 16 / (1 - a^2)

Equate these:

16 / (1 - a^2) = 10 / (1 - a)
16 (1 - a) = 10 (1 - a^2)

16 - 16a = 10 - 10a^2
16 - 16a - 10 + 10a^2 = 0
10a^2 - 16a + 6 = 0
5a^2 - 8a + 3 = 0

Using the quadratic equation

a = [ -b +/- (b^2-4ac) ] / 2a = (8 +/- 2 ) / 10 = 1 or 3/5

(I get 2 solutions but the answer only gives 3/5. Don't see why the other isn't valid).

So substitute into the first recurrance relation to get L = 10 / (1 - 3/5) = 25

[Max018]

Hi,

Ah, brilliant! Yeah I got to the cross multiply bit but got a bit stumped after that. Could you explain a wee bit why you used b^2 - 4ac to get the two answers, I dont get this line:

[AndyW]

I didn't notice that it factorised easily, so I used the quadratic formula as here:

http://www.sosmath.com/algebra/quadraticeq...draformula.html

(in my message above b^2-4ac should have been (b^2-4ac)^1/2