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January 5th, 2009, 07:18 AM
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| |  factor theorem
Given that (x-3) and (2x+1) are factors of  , find the values of a and b . With these values of a and b , show that  for all x belongs to real numbers .
My working :
i found that a = 4 and b = -20  
I am wondering how can i show that from here .
Thanks for any help . |
January 5th, 2009, 07:27 AM
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Quote:
Originally Posted by mathaddict  Given that (x-3) and (2x+1) are factors of , find the values of a and b . With these values of a and b , show that for all x belongs to real numbers .
My working :
i found that a = 4 and b = -20
I am wondering how can i show that from here .
Thanks for any help . | I suggest you find the coordinates and nature of the turning points of y = f(x) (note that  .... )
__________________ There are two things you should never try to prove: the impossible and the obvious. The greater danger for most of us lies not in setting our aim too high and falling short; but in setting our aim too low and achieving our mark. (Michelangelo Buonarroti)
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January 5th, 2009, 10:15 AM
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I think f(x) not >=0 with all real numbers .Maybe the problem is wrong . |
January 5th, 2009, 01:30 PM
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Quote:
Originally Posted by fanfan1609 I think f(x) not >=0 with all real numbers .Maybe the problem is wrong . | You're wrong. On what grounds do you make this statement?
__________________ There are two things you should never try to prove: the impossible and the obvious. The greater danger for most of us lies not in setting our aim too high and falling short; but in setting our aim too low and achieving our mark. (Michelangelo Buonarroti)
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January 5th, 2009, 02:21 PM
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Quote:
Originally Posted by mathaddict Given that (x-3) and (2x+1) are factors of , find the values of a and b . With these values of a and b , show that for all x belongs to real numbers .
My working :
i found that a = 4 and b = -20
I am wondering how can i show that from here .
Thanks for any help . | Try factorising  . | | The Following 2 Users Say Thank You to Opalg For This Useful Post: | |  |
January 5th, 2009, 04:16 PM
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Quote:
Originally Posted by Opalg Try factorising . | Well, you only do that if you want to do it the easy way ..... 
__________________ There are two things you should never try to prove: the impossible and the obvious. The greater danger for most of us lies not in setting our aim too high and falling short; but in setting our aim too low and achieving our mark. (Michelangelo Buonarroti)
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January 5th, 2009, 04:30 PM
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Quote:
Originally Posted by mr fantastic You're wrong. On what grounds do you make this statement? | After factorising . I have  If x belongs (3/2,3) ,f(x) <0 .Example x=2 ,I have f(2)=(2-3).(2.2+1).(2.2-3).(2+1)=(-1).5.1.3=-15 I thinks so that . |
January 5th, 2009, 05:04 PM
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 .
If you had expanded as a check you would have noticed this.
__________________ There are two things you should never try to prove: the impossible and the obvious. The greater danger for most of us lies not in setting our aim too high and falling short; but in setting our aim too low and achieving our mark. (Michelangelo Buonarroti)
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January 5th, 2009, 08:43 PM
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Quote:
Originally Posted by mr fantastic .
If you had expanded as a check you would have noticed this. | Oh.I had a stupid mistake .Thanks for your check  If that ,  .so that f(x) >= 0 with all x belongs real numbers .
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