New Enroll in RBI Grade B New Batch - Starts on May 21

    Question

    Find the interval of x where the expression 21x - 3x² - 54

    is greater than zero.
    A 1 > x > 6 Correct Answer Incorrect Answer
    B 1 < x < 6 Correct Answer Incorrect Answer
    C 1 ≤ x ≤ 6 Correct Answer Incorrect Answer
    D 1 ≥ x ≥ 6 Correct Answer Incorrect Answer

    Solution

    ATQ,

    So, 21x - 3x² - 54 > 0

    Or, 3x² - 21x + 54 < 0

    Or, 3x² - 18x - 3x + 54 < 0

    Or, 3x(x - 6) -3(x - 6) < 0

    Or, (3x - 3)(x - 6) < 0

    So, x = 1 and x = 6

    Therefore, the expression is positive between 1 and 6.

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