SarkariPYQ

SSC CGL 2021 PYQ — Question 70

SSC CGL - 18 Aug 2021 - Shift 3 • Quantitative Aptitude • Q70

Back to paper

What is the constant term in the expansion of (5x2−1x)3?(5x^2 - \frac{1}{x})^3?

Show answer & explanation

Correct answer: A

Explanation

The correct answer is option 1 i.e. 15.

(5x2−1x)3(5x^2 - \frac{1}{x})^3 = [(5x3 - 1)/x]3

= (5x3)3−1−3×5x3×1(5x3−1)x3\frac{(5x^3)^3 - 1 - 3 \times 5x^3 \times 1(5x^3 - 1)}{x^3}

= 5x9−1−75x3+15x3x3\frac{5x^9 - 1 - 75x^3 + 15x^3}{x^3}

Now one can observe that the constant term will be 15.