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VCE Stuff => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Mathematics => Topic started by: lolaishappy on September 16, 2014, 06:20:39 pm

Title: Unit 2, question about derivatives
Post by: lolaishappy on September 16, 2014, 06:20:39 pm

Im new here, and I always need help  :'( ::)
so this is the question..

The function y=x^3(a/3) - x^2(b/2) + 6x + c  has turning points at x=1 and x=-1.
A) find the derivative..
which is    ax^2 -bx + 6

B) Find the values of a and b. Im stuck at this question  :-[

Title: Re: Unit 2, question about derivatives
Post by: theshunpo on September 16, 2014, 06:36:47 pm

At the turning points (x=1 and x=-1) (the derivative) is equal to 0.

Using x=1 and x=-1, you can create two simultaneous equations which equal to 0, which will allow you to solve for a and b.
These simultaneous equations are:

Spoiler

a-b+6=0 and a+b+6=0

Title: Re: Unit 2, question about derivatives
Post by: lolaishappy on September 16, 2014, 06:50:49 pm

Quote from: theshunpo on September 16, 2014, 06:36:47 pm

At the turning points (x=1 and x=-1) (the derivative) is equal to 0.

Using x=1 and x=-1, you can create two simultaneous equations which equal to 0, which will allow you to solve for a and b.
These simultaneous equations are:

Spoiler

a-b+6=0 and a+b+6=0

Thanks so much, much simpler than the teacher's way. 8)