// Numbas version: exam_results_page_options {"name": "Integration by Substitution", "extensions": [], "custom_part_types": [], "resources": [], "navigation": {"allowregen": true, "showfrontpage": false, "preventleave": false, "typeendtoleave": false}, "question_groups": [{"pickingStrategy": "all-ordered", "questions": [{"variable_groups": [], "preamble": {"js": "", "css": ""}, "ungrouped_variables": ["a", "b", "m"], "functions": {}, "extensions": [], "variablesTest": {"condition": "", "maxRuns": 100}, "metadata": {"description": "

Step by step solving for integration by substitution

", "licence": "Creative Commons Attribution 4.0 International"}, "statement": "

Integrate the following by substitution.

\n

Don't forget the constant of integration ($C$).

", "variables": {"b": {"templateType": "anything", "description": "", "definition": "repeat(random(-9..9 except 0),5)", "group": "Ungrouped variables", "name": "b"}, "m": {"templateType": "anything", "description": "", "definition": "repeat(random(4..9),5)", "group": "Ungrouped variables", "name": "m"}, "a": {"templateType": "anything", "description": "", "definition": "repeat(random(1..5),5)", "group": "Ungrouped variables", "name": "a"}}, "tags": [], "parts": [{"customName": "", "customMarkingAlgorithm": "", "sortAnswers": false, "scripts": {}, "prompt": "

$I=\\simplify[std]{Int( x*({a[0]}x^2+{b[0]})^{m[0]},x)}$

\n

\n

Use $u=\\simplify[std]{{a[0]}x^2+{b[0]}}$ as your substitution.

\n

$\\frac{du}{dx}=$ [[1]]

\n

$dx=$ [[2]]

\n

Substituting back into the original equation for $dx$ and pulling out constants gives

\n

$I=$[[3]]$\\simplify[std]{Int(u^{m[0]},u)}$

\n

The next step is to integrate.

\n

$\\simplify{Int(u^{m[0]},u)}=$ [[4]]

\n

Putting all of these results together, we get the final answer of:

\n

[[0]]

", "extendBaseMarkingAlgorithm": true, "showCorrectAnswer": true, "variableReplacementStrategy": "originalfirst", "type": "gapfill", "showFeedbackIcon": true, "marks": 0, "unitTests": [], "useCustomName": false, "gaps": [{"customName": "", "customMarkingAlgorithm": "", "failureRate": 1, "checkingType": "absdiff", "showCorrectAnswer": false, "checkVariableNames": false, "vsetRange": [0, 1], "showFeedbackIcon": true, "vsetRangePoints": 5, "notallowed": {"message": "

Input all numbers as integers or fractions and not as decimals.

", "showStrings": false, "strings": ["."], "partialCredit": 0}, "checkingAccuracy": 0.001, "scripts": {}, "answer": "(({a[0]}*(x^2)+{b[0]})^({m[0]}+1))/(2*{a[0]}*({m[0]}+1))+C", "valuegenerators": [{"value": "", "name": "c"}, {"value": "", "name": "x"}], "extendBaseMarkingAlgorithm": true, "variableReplacementStrategy": "originalfirst", "type": "jme", "answerSimplification": "all", "marks": "2", "unitTests": [], "showPreview": true, "useCustomName": false, "variableReplacements": []}, {"customName": "", "customMarkingAlgorithm": "", "failureRate": 1, "checkingType": "absdiff", "showCorrectAnswer": false, "checkVariableNames": false, "vsetRange": [0, 1], "showFeedbackIcon": true, "vsetRangePoints": 5, "checkingAccuracy": 0.001, "scripts": {}, "answer": "2{a[0]}x", "valuegenerators": [{"value": "", "name": "x"}], "extendBaseMarkingAlgorithm": true, "variableReplacementStrategy": "originalfirst", "type": "jme", "answerSimplification": "all", "marks": 1, "unitTests": [], "showPreview": true, "useCustomName": false, "variableReplacements": []}, {"customName": "", "customMarkingAlgorithm": "", "failureRate": 1, "checkingType": "absdiff", "showCorrectAnswer": false, "checkVariableNames": false, "vsetRange": [0, 1], "showFeedbackIcon": true, "vsetRangePoints": 5, "checkingAccuracy": 0.001, "scripts": {}, "answer": "du/(2{a[0]}x)", "valuegenerators": [{"value": "", "name": "du"}, {"value": "", "name": "x"}], "extendBaseMarkingAlgorithm": true, "variableReplacementStrategy": "originalfirst", "type": "jme", "answerSimplification": "all", "marks": "1", "unitTests": [], "showPreview": true, "useCustomName": false, "variableReplacements": []}, {"customName": "", "customMarkingAlgorithm": "", "correctAnswerStyle": "plain", "scripts": {}, "maxValue": "1/(2{a[0]})", "allowFractions": true, "mustBeReducedPC": 0, "extendBaseMarkingAlgorithm": true, "showFractionHint": true, "showCorrectAnswer": false, "variableReplacementStrategy": "originalfirst", "type": "numberentry", "showFeedbackIcon": true, "notationStyles": ["plain", "en", "si-en"], "marks": 1, "unitTests": [], "minValue": "1/(2{a[0]})", "useCustomName": false, "correctAnswerFraction": true, "variableReplacements": [], "mustBeReduced": false}, {"customName": "", "customMarkingAlgorithm": "", "failureRate": 1, "checkingType": "absdiff", "showCorrectAnswer": false, "checkVariableNames": false, "vsetRange": [0, 1], "showFeedbackIcon": true, "vsetRangePoints": 5, "checkingAccuracy": 0.001, "scripts": {}, "answer": "u^({m[0]}+1)/({m[0]}+1)", "valuegenerators": [{"value": "", "name": "u"}], "extendBaseMarkingAlgorithm": true, "variableReplacementStrategy": "originalfirst", "type": "jme", "answerSimplification": "all", "marks": "1", "unitTests": [], "showPreview": true, "useCustomName": false, "variableReplacements": []}], "variableReplacements": []}], "rulesets": {"std": ["all", "!collectNumbers", "fractionNumbers", "!noLeadingMinus"]}, "advice": "

This problem is best solved by using substitution.
Note that if we let $u=\\simplify[std]{{a[0]} * (x ^ 2) + {b[0]}}$ then $du=\\simplify[std]{(2*{a[0]} * x)*dx }$
Hence we can replace $xdx$ by $\\frac{1}{2*\\var{a[0]}}du$.

\n

Hence the integral becomes:

\n

\\[\\begin{eqnarray*} I&=&\\simplify[std]{Int((1/(2{a[0]}))u^{m[0]},u)}\\\\ &=&\\simplify[all]{(1/(2{a[0]}))u^{m[0]+1}/{m[0]+1}+C}\\\\ &=& \\simplify[all]{({a[0]} * (x ^ 2) + {b[0]})^{m[0]+1}/(2{a[0]}*({m[0]}+1))+C} \\end{eqnarray*}\\]

\n

A Useful Result
This example can be generalised.
Suppose \\[I = \\int\\; f'(x)g(f(x))\\;dx\\]
The using the substitution $u=f(x)$ we find that $du=f'(x)\\;dx$ and so using the same method as above:
\\[I = \\int g(u)\\;du \\]
And if we can find this simpler integral in terms of $u$ we can replace $u$ by $f(x)$ and get the result in terms of $x$.

", "name": "Integration by Substitution", "contributors": [{"name": "Kieran Mulchrone", "profile_url": "https://numbas.mathcentre.ac.uk/accounts/profile/1243/"}, {"name": "Xiaodan Leng", "profile_url": "https://numbas.mathcentre.ac.uk/accounts/profile/2146/"}]}]}], "contributors": [{"name": "Kieran Mulchrone", "profile_url": "https://numbas.mathcentre.ac.uk/accounts/profile/1243/"}, {"name": "Xiaodan Leng", "profile_url": "https://numbas.mathcentre.ac.uk/accounts/profile/2146/"}]}