a³ - 21a - 20 রাশিটির উৎপাদক নয় কোনটি?
Solution
Correct Answer: Option D
a3 - 21a - 20
= a3 + a2 - a2 - a - 20a - 20
= a2(a +1) - a (a + 1) - 20 (a + 1)
= (a + 1)(a2 - a - 20)
= (a + 1)(a2 - 5a + 4a − 20)
= (a + 1){a (a - 5) + 4 (a − 5)}
= (a + 1)(a - 5) (a + 4)
∴ (a + 2), a3 - 21a - 20 রাশিটির উৎপাদক নয়।
= a3 + a2 - a2 - a - 20a - 20
= a2(a +1) - a (a + 1) - 20 (a + 1)
= (a + 1)(a2 - a - 20)
= (a + 1)(a2 - 5a + 4a − 20)
= (a + 1){a (a - 5) + 4 (a − 5)}
= (a + 1)(a - 5) (a + 4)
∴ (a + 2), a3 - 21a - 20 রাশিটির উৎপাদক নয়।
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