JAMB 2016 Mathematics · Question 36

If y = 2x3 + 6x2 + 6x + 1, Find dydx\frac{dy}{dx}

Options

  1. A.6x2 + 12x + 1
  2. B.6x2 + 6x + 1
  3. C.6x2 + 6x + 6
  4. D.6x2 + 12x + 6

Answer: D. 6x2 + 12x + 6

Explanation written with AI and checked against the answer key

Analysis

The question asks for the derivative of the polynomial function y=2x3+6x2+6x+1y = 2x^3 + 6x^2 + 6x + 1 with respect to xx. This is a standard calculus problem involving the power rule for differentiation.

Concept: The Power Rule

To differentiate a term of the form axnax^n, you use the Power Rule:

ddx(axn)=n⋅axn−1\frac{d}{dx}(ax^n) = n \cdot ax^{n-1}

Essentially, you multiply the coefficient by the exponent and then subtract 1 from the exponent.

  • The derivative of a constant (like 1) is always 0.
  • The derivative of xx (which is x1x^1) is 1.
Step-by-Step Solution

Given the function:

y=2x3+6x2+6x+1y = 2x^3 + 6x^2 + 6x + 1

We differentiate each term individually:

  1. For 2x32x^3: Multiply 3 by 2 and subtract 1 from the exponent: 3×2x(3−1)=6x23 \times 2x^{(3-1)} = 6x^2
  1. For 6x26x^2: Multiply 2 by 6 and subtract 1 from the exponent: 2×6x(2−1)=12x1=12x2 \times 6x^{(2-1)} = 12x^1 = 12x
  1. For 6x6x: The derivative of 6x6x is simply the coefficient: 1×6x(1−1)=6x0=6(1)=61 \times 6x^{(1-1)} = 6x^0 = 6(1) = 6
  1. For 11: The derivative of any constant is 0.

Combining these results:

dydx=6x2+12x+6\frac{dy}{dx} = 6x^2 + 12x + 6
Conclusion

Comparing our result to the given options, we find that it matches option D.

Exam Tip: Always remember to differentiate the constant term! Many students mistakenly leave the constant in the final answer or forget to change it to zero. Also, double-check your arithmetic when multiplying the exponent by the coefficient—it's a common place for "silly" mistakes under exam pressure.

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