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deepaksoni
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Five times a certain whole number is equal to three less than twice the square of the number. Find the number.

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This question has been taken from Book:- ML aggarwal, Avichal publication, class10th, quadratic equation in one variable, chapter 5, exercise 5.5
This is an important ques and asked in paper

Five times a certain whole number is equal to three less than twice the square of the number. Find the number.
Question no. 4 , ML Aggarwal, chapter 5, exercise 5.5, quadratic equation in one variable, ICSE board,

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1 Answer

  1. Let us consider the number be ‘x’

    So according to the question,

    5x = 2x2 – 3

    2x2 – 3 – 5x = 0

    2x2 – 5x – 3 = 0

    Let us factorize,

    2x2 – 6x + x – 3 = 0

    2x(x – 3) + 1(x – 3) = 0

    (x – 3) (2x + 1) = 0

    So,

    (x – 3) = 0 or (2x + 1) = 0

    x = 3 or 2x = -1

    x = 3 or x = -1/2

    ∴ The required number is 3 [since, -1/2 cannot be a whole number].

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