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Factorise: X4 - 5x2 - 36 - Mathematics

Sum

Factorise: x4 - 5x2 - 36

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Solution

x4 - 5x2 - 36

= (x2)2 - 5x2 - 36

= (x2)2 - 9x2 + 4x2 - 36    ...{∵ -36 = -9 × 4 }
                                            {-5 = -9 + 4}

= x2 (x2 - 9) +  (x2 - 9)

= (x2 - 9)(x2 + 4)

= [x2 - (3)2] [x2 + 4]

= (x + 3)(x - 3)(x2 + 4)

= (x2 +4) (x + 3)(x - 3)  

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APPEARS IN

Selina Concise Mathematics Class 8 ICSE
Chapter 13 Factorisation
Exercise 13 (F) | Q 8.5 | Page 163
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