IGCSE/GCSE/O & A Level/IB/University Student Forum

Qualification => Subject Doubts => GCE AS & A2 Level => Math => Topic started by: osmosis on February 18, 2010, 03:14:56 pm

Title: I need help on question no. 2 Oct/Nov 2009 pure math 3
Post by: osmosis on February 18, 2010, 03:14:56 pm

can anyone help me how to find the two consecutive integers for question no.2 OCT/NOV 2009 pure math 3 paper??? ???

Title: Re: I need help on question no. 2 Oct/Nov 2009 pure math 3
Post by: osmosis on February 18, 2010, 03:49:23 pm

do we need to just substitute any integer??? or is there any other way to get x=3 and x=4???

Title: Re: I need help on question no. 2 Oct/Nov 2009 pure math 3
Post by: astarmathsandphysics on February 19, 2010, 12:16:36 am

Will answer when I get up

Title: Re: I need help on question no. 2 Oct/Nov 2009 pure math 3
Post by: astarmathsandphysics on February 19, 2010, 08:54:43 am

3^(x+2)=3^x+3^2
3^(x+2)-3^x=3^2
3^x(3^2-1)=3^2
3^x=3^2/(3^2-1)
xln3=ln(3^2/(3^2-1))
x=ln(3^2/(3^2-1)))/ln3

Title: Re: I need help on question no. 2 Oct/Nov 2009 pure math 3
Post by: osmosis on February 19, 2010, 12:35:21 pm

owh...that is for paper 31.... mine is paper 32....about finding the two consecutive integers on numerical solution topic.....that's where I got problem in finding the integer...can you help me with that one? :)

Title: Re: I need help on question no. 2 Oct/Nov 2009 pure math 3
Post by: astarmathsandphysics on February 19, 2010, 12:43:35 pm

How did I miss that? When I get home.

Title: Re: I need help on question no. 2 Oct/Nov 2009 pure math 3
Post by: astarmathsandphysics on February 19, 2010, 05:44:05 pm

Trial and error. The root is between 3 an 4
f(3)<0 f(4)>0
so between 3 and 4 there is a sign change and a root.

Title: Re: I need help on question no. 2 Oct/Nov 2009 pure math 3
Post by: osmosis on February 19, 2010, 10:47:16 pm

ok....thank you so much! :)