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Question

What is the square root of the following?
$(x^2 - 14x + 49)(x^2 + 6x + 9)$

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper PDF (31-Jan-2021) (Shift 1)
The correct answer is
$(x - 7)(x + 3)$

Factoring the Algebraic Expression

The expression provided is: $(x^2 - 14x + 49)(x^2 + 6x + 9)$

To find its square root, we first factor each quadratic part.

  • The first quadratic, $x^2 - 14x + 49$, is a perfect square trinomial. It factors as $(x - 7)^2$.
  • The second quadratic, $x^2 + 6x + 9$, is also a perfect square trinomial. It factors as $(x + 3)^2$.

Substituting these factors back, the expression becomes:

$(x - 7)^2 (x + 3)^2$

Calculating the Square Root

Now, we calculate the square root of this factored expression:

$\sqrt{(x - 7)^2 (x + 3)^2}$

Using the property $\sqrt{a^2 b^2} = \sqrt{a^2}\sqrt{b^2} = |a||b|$, we get:

$|x - 7| \times |x + 3|$

In algebraic contexts like this multiple-choice question, the principal square root is typically considered, simplifying to:

$(x - 7)(x + 3)$

This result matches Option B.

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Important Questions from Polynomials

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  2. Two circles have radius in the ratio \(4 : 3\), write a polynomial to express the combined total surface area of the two circles.
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