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April 17th, 2011, 04:24 PM  #1 
Newbie Joined: Mar 2011 Posts: 12 Thanks: 0  Solving Cubic Equations
Consider the polynomial p(x)=x³+ax²+bx12 Given that (x+3) and (x4) are factors of p(x), factorise p(x) completely. I'm not sure whether I should sub in 3 and 4 or whether I should divide the original polynomial by x+3 and x4. 
April 17th, 2011, 05:09 PM  #2  
Math Team Joined: Dec 2006 From: Lexington, MA Posts: 3,267 Thanks: 408  Re: Solving Cubic Equations Hello, chris99191! Quote:
This is how I solved it . . . [color=beige]. . [/color] [color=beige]. . [/color] [color=beige]. . [/color]  
April 17th, 2011, 06:06 PM  #3 
Global Moderator Joined: Dec 2006 Posts: 21,034 Thanks: 2271 
If x³ + ax² + bx  12 ? (x + 3)(x  4)(x + r), putting x = 0 gives r = 1.


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