Question
Factorise$ :a^4 - 343a$
✓
Answer
$a^4 - 343a$
$= a( a^3 - 7^3 )$
$= a( a - 7 )[(a)^2 + a x 7 + (7)^2 ] [ \because a^3 - b^3 = ( a - b )( a^2 + ab + b^2 )]$
$= a( a - 7 )( a^2 + 7a + 49 )$
$= a( a^3 - 7^3 )$
$= a( a - 7 )[(a)^2 + a x 7 + (7)^2 ] [ \because a^3 - b^3 = ( a - b )( a^2 + ab + b^2 )]$
$= a( a - 7 )( a^2 + 7a + 49 )$
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