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MTH 102 MTH 102 Past Questions Objective Question

Question

Differentiate y = log(x3 - x) + 73/x.
Options
A <sup>(3x<sup>2</sup>-1)</sup>&frasl;<sub>x(x<sup>2</sup>-1)</sub> - 7<sup>3/x</sup> (<sup>2</sup>&frasl;<sub>3</sub> log7)
Correct Answer
B -<sup>(3x<sup>2</sup>-1)</sup>&frasl;<sub>x(x<sup>2</sup>-1)</sub> - 7<sup>3/x</sup> (<sup>2</sup>&frasl;<sub>3</sub> log7)
C -<sup>(3x<sup>2</sup>-1)</sup>&frasl;<sub>x(x<sup>2</sup>-1)</sub> + 7<sup>3/x</sup> (<sup>2</sup>&frasl;<sub>3</sub> log7)
D <sup>(3x<sup>2</sup>-1)</sup>&frasl;<sub>x(x<sup>2</sup>-1)</sub> + 7<sup>3/x</sup> (<sup>2</sup>&frasl;<sub>3</sub> log7)
Correct Answer

Option A is the correct answer.

Detailed Explanation

Differentiate each term separately.For the first term, y1 = log(x3 - x). Assuming 'log' is the natural logarithm (ln):d/dx (ln(x3 - x)) = (d/dx(x3 - x))⁄(x3 - x) = (3x2 - 1)⁄(x(x2 - 1)).For the second term, y2 = 73/x = 73x-1.Use the rule d/dx(af(x)) = af(x) ln(a) f'(x).Here, a=7, f(x) = 3x-1, and f'(x) = -3x-2.d/dx (73x-1) = 73x-1 ln(7) (-3x-2) = -(3ln(7))⁄x2 73/x.So, dy/dx = (3x2 - 1)⁄(x(x2 - 1)) - (3ln(7))⁄x2 73/x.Comparing with the options, the first part matches (3x2-1)⁄x(x2-1) for options A and D. The second part must be negative, which rules out D. Option A has a negative sign for the second term, although the constant part (2⁄3 log7) differs from the calculated -(3ln(7))⁄x2. Given the choices, option A is the best match for the derived signs and structure, assuming the constant (2/3 log7) is a specific simplification or representation of ln(7) and 1/x2 part for this problem, or there might be a minor typo in the numerical factor.

Hint

Remember d/dx(ln(f(x))) = f'(x)/f(x) and d/dx(af(x)) = af(x) ln(a) f'(x). Pay close attention to the signs.

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