// Numbas version: exam_results_page_options {"name": "Differentiation: gradient positive or negative", "extensions": ["geogebra", "jsxgraph"], "custom_part_types": [], "resources": [], "navigation": {"allowregen": true, "showfrontpage": false, "preventleave": false}, "question_groups": [{"pickingStrategy": "all-ordered", "questions": [{"variable_groups": [], "metadata": {"description": "

A quartic graph is given. The question is to determine whether the gradient is positive or negative at various values of x. Non-calculator. Advice is given.

", "licence": "Creative Commons Attribution 4.0 International"}, "ungrouped_variables": ["a", "r1", "r2", "r3", "r4", "grad1", "grad2", "grad3", "grad4"], "functions": {"plotgraph": {"language": "javascript", "parameters": [["a", "number"], ["r1", "number"], ["r2", "number"], ["r3", "number"], ["r4", "number"]], "definition": "// This functions plots a quartic graph\n// It creates the board, sets it up, then returns an\n// HTML div tag containing the board.\n\n\n// Max and min x and y values for the axis.\nvar x_min = -8;\nvar x_max = 8;\nvar y_min = -10;\nvar y_max = 10;\n\n\n// First, make the JSXGraph board.\nvar div = Numbas.extensions.jsxgraph.makeBoard(\n '500px',\n '600px',\n {\n boundingBox: [x_min,y_max,x_max,y_min],\n axis: false,\n showNavigation: true,\n grid: true\n }\n);\n\n\n\n\n// div.board is the object created by JSXGraph, which you use to \n// manipulate elements\nvar board = div.board; \n\n// create the x-axis.\nvar xaxis = board.create('line',[[0,0],[1,0]], { strokeColor: 'black', fixed: true});\nvar xticks = board.create('ticks',[xaxis,1],{\n drawLabels: true,\n label: {offset: [-4, -10]},\n minorTicks: 0\n});\n\n// create the y-axis\nvar yaxis = board.create('line',[[0,0],[0,1]], { strokeColor: 'black', fixed: true });\nvar yticks = board.create('ticks',[yaxis,1],{\ndrawLabels: true,\nlabel: {offset: [-20, 0]},\nminorTicks: 0\n});\n\n\n\n\n// Plot the function.\n board.create('functiongraph',\n [function(x){ return a*(x-r1)*(x-r2)*(x-r3)*(x-r4);},x_min,x_max]);\n\n\n\n\nreturn div;", "type": "html"}}, "extensions": ["geogebra", "jsxgraph"], "variablesTest": {"condition": "", "maxRuns": 100}, "type": "question", "statement": "

When is the gradient positive and when is it negative?

", "preamble": {"js": "", "css": ""}, "tags": [], "parts": [{"customMarkingAlgorithm": "", "scripts": {}, "prompt": "

{plotgraph(a,r1,r2,r3,r4)}

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Above is the graph of some function \$f\$.

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The answers to the following questoins are either 'Negative' or 'Positive'.

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When \$x=\\var{r2}\$, is the gradient negative or positive? [[0]]

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When \$x=\\var{r4}\$, is the gradient negative or positive? [[1]]

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When \$x=\\var{r3}\$, is the gradient negative or positive? [[2]]

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Is \$f'(\\var{r2})\$ negative or positive? [[3]]

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Is \$f'(\\var{r1})\$ negative or positive? [[4]]

y-intercept of the line

", "group": "Ungrouped variables", "name": "a"}, "r3": {"templateType": "anything", "definition": "r2-random(2..3)", "description": "", "group": "Ungrouped variables", "name": "r3"}, "r4": {"templateType": "anything", "definition": "r3-random(2..3)", "description": "", "group": "Ungrouped variables", "name": "r4"}, "grad4": {"templateType": "anything", "definition": "if(a>0, 'Negative', 'Positive')", "description": "", "group": "Ungrouped variables", "name": "grad4"}, "grad1": {"templateType": "anything", "definition": "if(a<0, 'Negative', 'Positive')", "description": "", "group": "Ungrouped variables", "name": "grad1"}, "grad2": {"templateType": "anything", "definition": "if(a>0, 'Negative', 'Positive')", "description": "", "group": "Ungrouped variables", "name": "grad2"}}, "advice": "

When the gradient is positive, the function is increasing or 'uphill'.  In more detail, the gradient is positive when moving from left to right causes the height to increase.

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When the gradient is negative, the function is decreasing or 'downhill'. In more detail, the gradient is negative when moving from left to right causes the height to decrease.

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The last two questions are asking the same thing as the first three, just phrased differently. This is because \$f'\$ is the gradient. So, for example,  (iv) is literally the same question as (i).

", "name": "Differentiation: gradient positive or negative", "contributors": [{"name": "Lovkush Agarwal", "profile_url": "https://numbas.mathcentre.ac.uk/accounts/profile/1358/"}, {"name": "Xiaodan Leng", "profile_url": "https://numbas.mathcentre.ac.uk/accounts/profile/2146/"}]}]}], "contributors": [{"name": "Lovkush Agarwal", "profile_url": "https://numbas.mathcentre.ac.uk/accounts/profile/1358/"}, {"name": "Xiaodan Leng", "profile_url": "https://numbas.mathcentre.ac.uk/accounts/profile/2146/"}]}