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Using the Remainder Theorem, factorise the following completely: 3x3 + 2x2 – 23x – 30 - Mathematics

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प्रश्न

Using the Remainder Theorem, factorise the following completely:

3x3 + 2x2 – 23x – 30

बेरीज

उत्तर

f(x) = 3x3 + 2x2 – 23x – 30 

For x = –2, 

f(x) = f(–2)

= 3(–2)3 + 2(–2)2 – 23(–2) – 30 

= –24 + 8 + 46 – 30

= –54 + 54

= 0 

Hence, (x + 2) is a factor of f(x).

             3x2 – 4x – 15
`x + 2")"overline(3x^3 + 2x^2 - 23x - 30)`
           3x3 + 6x2                                            
                  – 4x2 – 23x
                  – 4x2 – 8x             
                           – 15x – 30
                           – 15x – 30    
                                    0
∴ 3x3 + 2x2 – 23x – 30 = (x + 2)(3x2 – 4x – 15) 

= (x + 2)(3x2 + 5x – 9x – 15)

= (x + 2)[x(3x + 5) – 3(3x + 5)] 

= (x + 2)(3x + 5)(x – 3)

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पाठ 8: Remainder and Factor Theorems - Exercise 8 (B) [पृष्ठ ११२]

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सेलिना Mathematics [English] Class 10 ICSE
पाठ 8 Remainder and Factor Theorems
Exercise 8 (B) | Q 2.3 | पृष्ठ ११२

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