Derivative of \( \displaystyle \frac{x}{2} - \frac{\sin{\left(4 x \right)}}{8} \)
Problem 2.32 · hard
Differentiate \( \displaystyle f(x) = \frac{x}{2} - \frac{\sin{\left(4 x \right)}}{8} \).
- \[ \frac{d}{d x} \left(\frac{x}{2} - \frac{\sin{\left(4 x \right)}}{8}\right) \]derivativeStart with the derivative of the function.✓ Proved
- \[ = \frac{d}{d x} \frac{x}{2} - \frac{d}{d x} \frac{\sin{\left(4 x \right)}}{8} \]sumApply the sum rule for differentiation.✓ Proved
- \[ = \frac{d}{d x} \frac{x}{2} - \frac{\frac{d}{d x} \sin{\left(4 x \right)}}{8} \]constantPull out the constant factor from the second term.✓ Proved
- \[ = - \frac{\cos{\left(4 x \right)} \frac{d}{d x} 4 x}{8} + \frac{d}{d x} \frac{x}{2} \]chainApply the chain rule to the sine term.✓ Proved
- \[ = - \frac{\cos{\left(4 x \right)}}{2} + \frac{d}{d x} \frac{x}{2} \]derivative algebraDifferentiate the inner function 4*x. Simplify the constant coefficients.✓ Proved
- \[ = \frac{1}{2} - \frac{\cos{\left(4 x \right)}}{2} \]derivativeEvaluate the derivative of the first term.✓ Proved
- \[ = 0.5 - 0.5 \cos{\left(4 x \right)} \]simplifyFinal simplified form.✓ Proved
Answer \( \frac{1}{2} - \frac{\cos{\left(4 x \right)}}{2} \)
✓ Nihil obstat Every line of this solution was proved by the computer algebra system SymPy. The answer was also checked a second way, without looking at the solution. Reviewers found nothing wrong with the explanation.
The full receipt
| Line | Status | Checked by | Detail |
|---|---|---|---|
| 1 | ✓ Proved | sympy 1.14.0 | line 1 is the problem as stated |
| 2 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 |
| answer | ✓ Proved | sympy 1.14.0 | final line against the stated answer: simplify(a - b) reduced to 0 |
| answer, a second way | ✓ Proved | sympy 1.14.0 | SymPy differentiated f directly and got the stated answer |
Reviewers
gpt-oss:20b: passdeepseek-r1:70b: passqwen3.6:27b-mlx: pass
Every verdict on record (12)
qwen3.6:27b-mlx: pass 2026-09-20gpt-oss:20b: pass 2026-09-20qwen3.6:27b-mlx: fail (style) 2026-09-20 — Step 3 is labeled 'constant' but pulls out a constant factor, which corresponds to the 'constant-multiple' rule in the fixed vocabulary. Step 2 is labeled 'sum' but applies the difference rule; while 'sum' is often used for linearity, the contract specifies 'sum' is acceptable for difference, so this is less severe, but the 'constant' vs 'constant-multiple' distinction is a clear vocabulary error.gpt-oss:20b: pass 2026-09-20qwen3.6:27b-mlx: fail (style) 2026-09-19 — Step 3 is labeled 'constant' but pulls out a constant factor, which should be labeled 'constant-multiple'. Step 7 is labeled 'derivative' but evaluates the derivative of x/2, which is correct, but the label 'derivative' is typically reserved for unfolding known derivatives; however, the main issue is Step 3's label. Actually, looking closer, Step 3 applies the constant multiple rule. The vocabulary has 'constant-multiple'. The step is labeled 'constant'. This is a labeling defect. Also, Step 2 is labeled 'sum' but it is a difference. The vocabulary says 'sum' covers difference. That is acceptable. Step 3 label 'constant' is incorrect; it should be 'constant-multiple'. Step 7 label 'derivative' is acceptable for evaluating d/dx(x/2). Step 6 label 'algebra' is acceptable. The primary defect is the label in Step 3.deepseek-r1:70b: pass 2026-09-19gpt-oss:20b: pass 2026-09-19qwen3.6:27b-mlx: pass 2026-09-19deepseek-r1:70b: pass 2026-09-19gpt-oss:20b: pass 2026-09-19gpt-oss:20b: fail 2026-09-17 — Step 2 incorrectly labels the rule as a sum rule; it should be the linearity rule for a difference.deepseek-r1:70b: pass 2026-09-17
Proved: SymPy reduced the difference between the two sides to zero. Checked independently: a separate
method, named above, confirmed it. Checked numerically: the two sides agree at every sampled point, which is evidence,
not proof. Reviewed: a model or a person read it; that is all a sentence can have. Solution by
gemma4:26b, checked 2026-09-26 with SymPy 1.14.0.