Derivative of \( \displaystyle \tan{\left(x \right)} \)
Problem 2.36 · easy
Differentiate \( \displaystyle f(x) = \tan{\left(x \right)} \).
- \[ \frac{d}{d x} \tan{\left(x \right)} \]derivativeStart with the derivative of the function.✓ Proved
- \[ = \frac{d}{d x} \frac{\sin{\left(x \right)}}{\cos{\left(x \right)}} \]rewrite productRewrite tan(x) as sin(x)/cos(x). Rewrite the quotient as a product.✓ Proved
- \[ = \sin{\left(x \right)} \frac{d}{d x} \frac{1}{\cos{\left(x \right)}} + \frac{\frac{d}{d x} \sin{\left(x \right)}}{\cos{\left(x \right)}} \]productApply the product rule.✓ Proved
- \[ = \sin{\left(x \right)} \frac{d}{d x} \frac{1}{\cos{\left(x \right)}} + 1 \]derivative rewriteDifferentiate sin(x). Rewrite 1/cos(x) as cos(x)**(-1).✓ Proved
- \[ = - \frac{\sin{\left(x \right)} \frac{d}{d x} \cos{\left(x \right)}}{\cos^{2}{\left(x \right)}} + 1 \]chainApply the chain rule to cos(x)**(-1).✓ Proved
- \[ = \frac{\sin^{2}{\left(x \right)}}{\cos^{2}{\left(x \right)}} + 1 \]derivative algebra algebra algebra algebraDifferentiate cos(x). Simplify the signs and terms. Rearrange the terms. Rewrite the negative exponent. Combine the fraction.✓ Proved
- \[ = \tan^{2}{\left(x \right)} + 1 \]rewriteRewrite the fraction as tan(x).✓ Proved
- \[ = \sec^{2}{\left(x \right)} \]simplifyUse the trigonometric identity 1 + tan(x)**2 = sec(x)**2.✓ Proved
Answer \( \tan^{2}{\left(x \right)} + 1 \)
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.
✓ 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 tan has poles at odd multiples of pi/2 undefined where cos(x) = 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where cos(x) = 0 |
| 4 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where cos(x) = 0 |
| 5 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where cos(x) = 0 |
| 6 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where cos(x) = 0 |
| 7 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where cos(x) = 0 |
| 8 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where cos(x) = 0 |
| 9 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where cos(x) = 0 |
| 10 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where cos(x) = 0 |
| 11 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where cos(x) = 0 |
| 12 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where cos(x) = 0 |
| 13 | ✓ Proved | sympy 1.14.0 | simplify(a - b) reduced to 0 undefined where cos(x) = 0 tan has poles at odd multiples of pi/2 |
| 14 | ✓ 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 |
| 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
gpt-oss:20b: passdeepseek-r1:70b: fail (style) — Step 3 mislabels a rewrite as a product rule.qwen3.6:27b-mlx: fail (style) — Step 3 applies two rules at once: it rewrites 1/cos(x) as a product factor and implicitly prepares for the product rule, but the label 'product' is incorrect for a rewriting step that does not yet apply the differentiation rule. The step should be labeled 'rewrite' or split into a rewrite step followed by a product rule step.
Every verdict on record (12)
qwen3.6:27b-mlx: fail (style) 2026-09-20 — Step 3 applies two rules at once: it rewrites 1/cos(x) as a product factor and implicitly prepares for the product rule, but the label 'product' is incorrect for a rewriting step that does not yet apply the differentiation rule. The step should be labeled 'rewrite' or split into a rewrite step followed by a product rule step.gpt-oss:20b: pass 2026-09-20qwen3.6:27b-mlx: pass 2026-09-20 — The solution correctly applies the product rule, chain rule, and trigonometric identities in distinct steps. The final simplification to sec(x)**2 is a valid equivalent form, even though the stated answer was tan(x)**2 + 1.gpt-oss:20b: pass 2026-09-20qwen3.6:27b-mlx: pass 2026-09-19 — The solution correctly applies the product rule and chain rule in separate steps, adhering to the one-change-per-step constraint. The labels accurately reflect the operations performed.deepseek-r1:70b: fail (style) 2026-09-19 — Step 3 mislabels a rewrite as a product rule.gpt-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 3 incorrectly labels the operation as a product rule; it is merely a rewrite of sin(x)/cos(x) into sin(x)*(1/cos(x)).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.