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

Qualification => Subject Doubts => GCE AS & A2 Level => Math => Topic started by: spiderman on October 16, 2009, 03:38:15 am

Title: Quadratics query
Post by: spiderman on October 16, 2009, 03:38:15 am

Hey guys,

pls can ull help me out with this question......

a) Express 9x^2+12x+7 in the form (ax+b)^2 + c where a,b and c are constants whose values are to be found.


b) Find the set of values taken by 1/(9x^2+12x+7) for real values of x.


Someone pls helppppp. ???

Title: Re: Quadratics query
Post by: nid404 on October 16, 2009, 07:56:31 am

a) is completing the square method

so it is (3x+2)²+3

b) 0<f(x)<=1/3
this is becuz no value of f(x) can be less than zero....since a negative x will be squared to give a positive value...
the greatest value of f(x) would be when denominator is least...this will be possible only when denominator is 3 and bracket is 0. hence 1/3

Title: Re: Quadratics query
Post by: spiderman on October 19, 2009, 07:23:00 am

Thanks a lot

Title: Re: Quadratics query
Post by: nid404 on October 21, 2009, 11:54:14 am

Quote from: spiderman on October 19, 2009, 07:23:00 am

Thanks a lot

ur welcome.