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

Qualification => Subject Doubts => GCE AS & A2 Level => Math => Topic started by: cashem'up on March 30, 2011, 10:58:42 pm

Title: Further Maths Question method
Post by: cashem'up on March 30, 2011, 10:58:42 pm

Show that the sum of the cubes of the roots of the equation
x3 + ? x + 1 = 0
is ?3.
Show also that there is no real value of ? for which the sum of the fourth powers of the roots is
negative.

ANSWER: The majority of candidates worked from S3 + ?S1 + 3 = 0
Alternatively, there were those who used the substitution X^3=Y

Now in most of these type of the questions i am only aware of the sub method... but what is the first method... can someone please explain me... the one regardin summation nd etc

Title: Re: Further Maths Question method
Post by: elemis on March 31, 2011, 05:27:01 am

What is does the question mark stand for ?

Can you rewrite the question ? Only then will I be able to answer it.

Title: Re: Further Maths Question method
Post by: cashem'up on March 31, 2011, 07:00:41 pm

Quote from: Ari Ben Canaan on March 31, 2011, 05:27:01 am

What is does the question mark stand for ?

Can you rewrite the question ? Only then will I be able to answer it.

? is B (a contant)
Show that the sum of the cubes of the roots of the equation
x3 + B x + 1 = 0
is minus 3.
Show also that there is no real value of B for which the sum of the fourth powers of the roots is
negative.

ANSWER: The majority of candidates worked from S3 + BS1 + 3 = 0
Alternatively, there were those who used the substitution X^3=Y

Now in most of these type of the questions i am only aware of the substitution method... but what is the first method... can someone please explain me... the one regardin summation nd etc

Title: Re: Further Maths Question method
Post by: astarmathsandphysics on April 01, 2011, 11:17:40 am

When I get to pc

Title: Re: Further Maths Question method
Post by: astarmathsandphysics on April 02, 2011, 07:25:16 am

1st part

Title: Re: Further Maths Question method
Post by: astarmathsandphysics on April 02, 2011, 07:36:33 am

contradiction the sum of 4th powers positive see attach

Title: Re: Further Maths Question method
Post by: cashem'up on April 02, 2011, 01:58:22 pm

Thanku very very much :D...cleared everything