// Numbas version: finer_feedback_settings {"name": "Luis's copy of Implicit differentiation", "timing": {"allowPause": true, "timedwarning": {"message": "", "action": "none"}, "timeout": {"message": "", "action": "none"}}, "navigation": {"onleave": {"message": "", "action": "none"}, "showfrontpage": true, "preventleave": true, "showresultspage": "oncompletion", "browse": true, "reverse": true, "allowregen": true}, "allQuestions": true, "duration": 0, "type": "exam", "questions": [], "shuffleQuestions": false, "feedback": {"showactualmark": true, "showanswerstate": true, "advicethreshold": 0, "allowrevealanswer": true, "showtotalmark": true, "enterreviewmodeimmediately": true, "showexpectedanswerswhen": "inreview", "showpartfeedbackmessageswhen": "always", "showactualmarkwhen": "always", "showtotalmarkwhen": "always", "showanswerstatewhen": "always", "showadvicewhen": "never"}, "metadata": {"notes": "", "description": "
Find $\\frac{\\mathrm{d}y}{\\mathrm{d}x}$ by differentiating an implicit equation.
", "licence": "Creative Commons Attribution 4.0 International"}, "percentPass": 0, "showQuestionGroupNames": false, "pickQuestions": 0, "question_groups": [{"questions": [{"name": "Implicit differentiation", "extensions": [], "custom_part_types": [], "resources": [], "navigation": {"allowregen": true, "showfrontpage": false, "preventleave": false, "typeendtoleave": false}, "contributors": [{"name": "Newcastle University Mathematics and Statistics", "profile_url": "https://numbas.mathcentre.ac.uk/accounts/profile/697/"}], "variable_groups": [], "variables": {"b": {"templateType": "anything", "group": "Ungrouped variables", "definition": "random(1..9)", "description": "", "name": "b"}, "a": {"templateType": "anything", "group": "Ungrouped variables", "definition": "-random(1..9)", "description": "", "name": "a"}, "c": {"templateType": "anything", "group": "Ungrouped variables", "definition": "random(1..9)", "description": "", "name": "c"}}, "ungrouped_variables": ["a", "c", "b"], "question_groups": [{"pickingStrategy": "all-ordered", "questions": [], "name": "", "pickQuestions": 0}], "functions": {}, "showQuestionGroupNames": false, "parts": [{"scripts": {}, "gaps": [{"answer": "(({( - a)} + ( - (2 * x))) / ({b} + (2 * y)))", "showCorrectAnswer": true, "vsetrange": [0, 1], "checkingaccuracy": 0.001, "checkvariablenames": false, "expectedvariablenames": [], "showpreview": true, "checkingtype": "absdiff", "scripts": {}, "type": "jme", "answersimplification": "all,!collectNumbers", "marks": 2, "vsetrangepoints": 5}], "type": "gapfill", "prompt": "\nUsing implicit differentiation find $\\displaystyle \\frac{dy}{dx}$ in terms of $x$ and $y$.
\nInput your answer here:
\n$\\displaystyle \\frac{dy}{dx}= $ [[0]]
\n ", "showCorrectAnswer": true, "marks": 0}], "statement": "Given the following relation between $x$ and $y$
\\[\\simplify[all,!collectNumbers]{x^2+y^2+{a}x+{b}y}=\\var{c}\\]
answer the following question.
20/06/2012:
\n \t\tAdded tags.
\n \t\tImproved display using \\displaystyle where appropriate.
\n \t\tChanged marks to 2.
\n \t\t\n \t\t
3/07/2012:
Added tags.
\n \t\t", "licence": "Creative Commons Attribution 4.0 International", "description": "\n \t\tImplicit differentiation.
\n \t\tGiven $x^2+y^2+ax+by=c$ find $\\displaystyle \\frac{dy}{dx}$ in terms of $x$ and $y$.
\n \t\t\n \t\t"}, "variablesTest": {"condition": "", "maxRuns": 100}, "advice": "
On differentiating both sides of the equation implicitly we get
\\[2x + \\simplify[all,!collectNumbers]{2y*Diff(y,x,1) + {a} + {b} *Diff(y,x,1)} = 0\\]
Collecting terms in $\\displaystyle\\frac{dy}{dx}$ and rearranging the equation we get
\\[(\\var{b} + 2y) \\frac{dy}{dx} = \\simplify[all,!collectNumbers]{{ -a} -2x}\\] and hence on further rearranging:
\\[\\frac{dy}{dx} = \\simplify[all,!collectNumbers]{({ - a} - 2 * x) / ({b} + (2 * y))}\\]