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    If the remainder on division of x³ + 2x² + kx + 3 by x – 3 is 21, then the value of k is:
    Question

    If the remainder on division of x³ + 2x² + kx + 3 by x – 3 is 21, then the value of k is:

    A.

    9

    B.

    - 9

    C.

    D.

    - 2

    Correct option is B

    Given:

    Polynomial: x³ + 2x² + kx + 3
    Divisor: x - 3
    Remainder: 21

    Concept used:
    Remainder Theorem: If a polynomial f(x) is divided by (x - a), then the remainder is f(a).

    Formula used:
    f(3) = 21

    Solution:
    Let f(x) = x³ + 2x² + kx + 3
    Then, f(3) = 3³ + 2(3)² + 3k + 3 = 21
    => 27 + 18 + 3k + 3 = 21
    => 48 + 3k = 21
    => 3k = 21 - 48 = -27
    => k = -9

    Correct answer is (b)

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