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

    Question

    Between what values of x is the expression 18x - 3x² - 45

    positive?
    A 1 > x > 5 Correct Answer Incorrect Answer
    B 1 < x < 5 Correct Answer Incorrect Answer
    C 1 ≤ x ≤ 5 Correct Answer Incorrect Answer
    D 1 ≥ x ≥ 5 Correct Answer Incorrect Answer

    Solution

    ATQ,

    So, 18x - 3x² - 45 > 0

    Or, 3x² - 18x + 45 < 0

    Or, 3x² - 15x - 3x + 45 < 0

    Or, 3x(x - 5) -3(x - 5) < 0

    Or, (3x - 3)(x - 5) < 0

    So, x = 1 or x = 5

    For any value of 'x' > 5, the expression becomes positive.

    So, 'x' lies between 1 and 5.

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