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

Qualification => Subject Doubts => GCE AS & A2 Level => Math => Topic started by: ashwinkandel on September 29, 2011, 03:32:56 pm

Title: Questions related to Quadratics
Post by: ashwinkandel on September 29, 2011, 03:32:56 pm

Find the range of value of c, given that, for all values of x, x^2+5x+c>2

Title: Re: Questions related to Quadratics
Post by: ........ on October 01, 2011, 06:47:37 pm

c>33/4

Title: Re: Questions related to Quadratics
Post by: ashwinkandel on October 02, 2011, 04:05:15 am

Can you show me the process?? how did u take out the answer

Title: Re: Questions related to Quadratics
Post by: astarmathsandphysics on October 02, 2011, 07:38:07 am

Complet the squuare
x^2+5x+c>2
(x+2.5)^2-2.5^2+c>2
(x+2.5)^2-2.5^2+c-2>0
(x+2.5)^2 is a square number so must be greater than zero, so
-2.5^2+c-2>0 so c>2.5^2+2=8.25

Title: Re: Questions related to Quadratics
Post by: ashwinkandel on October 02, 2011, 08:01:37 am

I am little bit confused with the last steps of the solution:
(x+2.5)^2 is a square number so must be greater than zero, so
-2.5^2+c-2>0 so c>2.5^2+2=8.25
I accept that (x+2.5)^2 is always greater than zero, then how can we say that -2.5^2+c-2 is also greater than zero?

Title: Re: Questions related to Quadratics
Post by: ashwinkandel on October 02, 2011, 08:18:49 am

Can you also give a glance to this question: (http://i53.tinypic.com/16gk02t.png)

Title: Re: Questions related to Quadratics
Post by: astarmathsandphysics on October 02, 2011, 08:23:56 am

Do you mean the question in black written in the black rectangle?

Title: Re: Questions related to Quadratics
Post by: astarmathsandphysics on October 02, 2011, 08:29:45 am

Because if (x+2.5)^2>0 sub (x+2.5)^2=00 into (x+2.5)^2-6.25+2-2>0 then solve for c

Title: Re: Questions related to Quadratics
Post by: ashwinkandel on October 02, 2011, 08:50:04 am

Thanks for clarification and yes, i mean the question in the  black rectangle

Title: Re: Questions related to Quadratics
Post by: astarmathsandphysics on October 02, 2011, 09:25:58 am

I can't read it.

Title: Re: Questions related to Quadratics
Post by: ashwinkandel on October 02, 2011, 09:36:05 am

Right click the image and click view image or just go to http://i53.tinypic.com/16gk02t.png (http://i53.tinypic.com/16gk02t.png)

Title: Re: Questions related to Quadratics
Post by: astarmathsandphysics on October 02, 2011, 09:47:59 am

A is 3 b is 2
Is there a diagram or min or max value of the function

Title: Re: Questions related to Quadratics
Post by: ashwinkandel on October 02, 2011, 09:54:42 am

Max. Value of the function is given in the next part and diagram is asked to be drawn. I am still confused how you took out the value of a as 3.