Derivative of \( \displaystyle - x + \tan{\left(x \right)} \)
Problem 2.11 · medium
Differentiate \( \displaystyle f(x) = - x + \tan{\left(x \right)} \).
- \[ \frac{d}{d x} \left(- x + \tan{\left(x \right)}\right) \]derivativeStart with the derivative of the function.✓ Proved
- \[ = \frac{d}{d x} \left(- x\right) + \frac{d}{d x} \tan{\left(x \right)} \]sumApply the sum rule.✓ Proved
- \[ = - \frac{d}{d x} x + \frac{d}{d x} \tan{\left(x \right)} \]constantApply the constant multiple rule to the first term.✓ Proved
- \[ = \frac{d}{d x} \tan{\left(x \right)} - 1 \]derivativeDifferentiate the first term.✓ Proved
- \[ = \sec^{2}{\left(x \right)} - 1 \]trig algebraDifferentiate the tangent function. Rearrange the terms.✓ Proved
Answer \( \tan^{2}{\left(x \right)} \)
Mind the domain. The answer is also defined at points where f(x) is not. Substituting there gives a number that is not a slope of f.
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. The reviewers disagree about how one step is explained; every verdict is in the receipt.
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 tan has poles at odd multiples of pi/2 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 tan has poles at odd multiples of pi/2 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 tan has poles at odd multiples of pi/2 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 tan has poles at odd multiples of pi/2 sec has poles at odd multiples of pi/2 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 sec has poles at odd multiples of pi/2 |
| answer | ✓ Proved | sympy 1.14.0 | final line against the stated answer: simplify(a - b) reduced to 0 tan has poles at odd multiples of pi/2 |
| answer, a second way | ✓ Proved | sympy 1.14.0 | SymPy differentiated f directly and got the stated answer |
Reviewers
deepseek-r1:70b: passgpt-oss:20b: passqwen3.6:27b-mlx: pass
Every verdict on record (14)
qwen3.6:27b-mlx: pass 2026-09-20gpt-oss:20b: pass 2026-09-20qwen3.6:27b-mlx: pass 2026-09-20gpt-oss:20b: fail (style) 2026-09-20 — Step 6 rearranges -1+sec(x)**2 to sec(x)**2-1 using the trigonometric identity sec^2(x)-1=tan^2(x). The label "algebra" is inappropriate; it should be "trig" (or a specific identity rule).qwen3.6:27b-mlx: pass 2026-09-19deepseek-r1:70b: pass 2026-09-19gpt-oss:20b: fail (error) 2026-09-19 — The solution stops at sec(x)**2 - 1, but the required final answer is tan(x)**2. The identity sec^2(x)-1 = tan^2(x) is missing, so the solution is incomplete and mathematically incorrect.qwen3.6:27b-mlx: pass 2026-09-19deepseek-r1:70b: pass 2026-09-19gpt-oss:20b: pass 2026-09-19qwen3.6:27b-mlx: pass 2026-09-18deepseek-r1:70b: pass 2026-09-18gpt-oss:20b: pass 2026-09-18deepseek-r1:70b: pass 2026-09-16
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.