Question

The factorisation of $a^4-125a$ is equal to .

• A. $a(a-5)(a^2+5a+25)$
• B. $a(a-5)(a^2+5a-25)$
• C. $a(a+5)(a^2+5a+25)$
• D. $a(a+5)(a^2-5a+25)$

Answer 1

The correct option is A $a(a-5)(a^2+5a+25)$

The given expression is $a^4-125a$
Taking out 'a' we get
$a(a^3-125)$
= $a(a^3-5^3)$
= $a(a-5)(a^2+5a+5^2)$ .... [$a^3-b^3=(a-b)(a^2+ab+b^2)$]
= $a(a-5)(a^2+5a+25)$