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On dividing 3x^3 + x^2 + 2x + 5 is divided by a polynomial g(x), the quotient and remainder are (3x – 5) and (9x + 10) respectively. Find g(x).

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Question

On dividing 3x3 + x2 + 2x + 5 is divided by a polynomial g(x), the quotient and remainder are (3x – 5) and (9x + 10) respectively. Find g(x).

Sum
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Solution

By using division rule, we have

Dividend = Quotient × Divisor + Remainder 

∴ 3x3 + x2 + 2x + 5 = (3x – 5)g(x) + 9x + 10

⇒ 3x3 + x2 + 2x + 5 – 9x – 10 = (3x – 5)g(x)

⇒ 3x3 + x2 – 7x – 5 = (3x – 5)g(x) 

⇒ `g(x) = (3x^3 + x^2 - 7x - 5)/(3x - 5)`  

                x2 + 2x + 1
`3x - 5")"overline(3x^3 + x^2 - 7x - 5)`
            3x3 – 5x2
            –       +                      
               6x2 –   7x – 5
               6x2 – 10x
            –       +                      
                          3x – 5
                          3x – 5
                       –      +             
                             x               

  ∴ g(x) = x2 + 2x + 1 

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Chapter 2: Polynomials - EXERCISE 2B [Page 63]

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R.S. Aggarwal Mathematics [English] Class 10
Chapter 2 Polynomials
EXERCISE 2B | Q 11. | Page 63

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