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When the Polynomial X3 + 2x2 – 5ax – 7 is Divided by (X – 1), the Remainder is a and When Polynomial X3 + Ax2 – 12x + 16 is Divided by (X + 2), the Remainder is B. Find the Value of ‘A’ If 2a + B = 0. - ICSE Class 10 - Mathematics

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Question

When the polynomial x3 + 2x2 – 5ax – 7 is divided by (x – 1), the remainder is A and when the polynomial x3 + ax2 – 12x + 16 is divided by (x + 2), the remainder is B. Find the value of ‘a’ if 2A + B = 0.

Solution

It is given that when the polynomial x3 + 2x2 – 5ax – 7 is divided by (x – 1), the remainder is A.
 ∴ (1)3 + 2(1)2 – 5a(1) – 7 = A
1 + 2 – 5a – 7 = A
– 5a – 4 = A …(i)
It is also given that when the polynomial x3 + ax2 – 12x + 16 is divided by (x + 2), the remainder is B.
 ∴ x3 + ax2 – 12x + 16 = B
(-2)3 + a(-2)2 – 12(-2) + 16 = B
-8 + 4a + 24 + 16 = B
4a + 32 = B …(ii)
It is also given that 2A + B = 0
Using (i) and (ii), we get,
2(-5a – 4) + 4a + 32 = 0
-10a – 8 + 4a + 32 = 0
-6a + 24 = 0
6a = 24
a = 4

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Solution When the Polynomial X3 + 2x2 – 5ax – 7 is Divided by (X – 1), the Remainder is a and When Polynomial X3 + Ax2 – 12x + 16 is Divided by (X + 2), the Remainder is B. Find the Value of ‘A’ If 2a + B = 0. Concept: Remainder Theorem.
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