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(i) To find \$f(\\var{x1})\$, you start at \$\\var{x1}\$ on the \$x\$-axis, go up or down until you reach the blue line, and then look at the \$y\$-coordinate. This \$y\$-coordinate is the answer.  In this question, after going up/down from \$\\var{x1}\$, we reach the \$y\$-coordinate \$\\var{y1}\$, so the answer is \$f(\\var{x1})=\\var{y1}\$.

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(ii) There are two options. The first option (which is not efficient) is trial-and-error: pick some random value of \$x\$ and determine \$f(x)\$. If \$f(x) = \\var{y2}\$, then your pick is the answer.  If not, then try a different value of \$x\$, hopefully getting closer and closer each time.   The second (and better) option is to 'work backwards' - we know what \$f(x)\$ should be, which means we know what the \$y\$-coordinate should be.  So start at \$\\var{y2}\$ on the \$y\$-axis, go left or right until you reach the blue line, and look at the \$x\$-coordinate. In this question, after going left/right from \$\\var{y2}\$, we reach the \$x\$-coordinate \$\\var{x2}\$, so this is the answer.  You can check this is correct: what is \$f(\\var{x2})\$? It is \$\\var{y2}\$, as we wanted!

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(iii) This question is asking exactly the same thing as the question in (ii), but is phrased differently. This is because the definition of \$f^{-1}\$ is that it is the function which un-does what \$f\$ does.  For example, we know that \$f(\\var{x1})=\\var{y1}\$ - therefore, automatically, \$f^{-1}(\\var{y1})\$ has to be \$\\var{x1}\$.  Re-worded, \$f\$ maps \$\\var{x1}\$ to \$\\var{y1}\$, so because \$f^{-1}\$ un-does this, it means \$f^{-1}\$ maps \$\\var{y1}\$ back to \$\\var{x1}\$.   Back to the question at hand, it asked what \$f^{-1}(\\var{y2})\$ is.  By definition, this means we want to know what value of \$x\$ is needed to get \$f(x) = \\var{y2}\$, which is exactly what was asked in (ii).

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{eqnline(a, hshift, vshift)}

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

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What is \$f(\\var{x1})\$? [[0]]

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What value of \$x\$ do you need to get \$f(x) = \\var{y2}\$? [[1]]

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What is \$f^{-1}(\\var{y2})\$? [[2]]

A graph of an (invertible) cubic is given. The question is to determine values of \$f\$ from graph.

", "licence": "Creative Commons Attribution 4.0 International"}, "variables": {"vshift": {"templateType": "anything", "description": "

Random amount of vertifical shift for sake of variability.

", "definition": "random(-2..2)", "group": "Ungrouped variables", "name": "vshift"}, "x1": {"templateType": "anything", "description": "", "definition": "random(0..1)", "group": "Ungrouped variables", "name": "x1"}, "a": {"templateType": "anything", "description": "

Coefficient of x^3

", "definition": "random(-1..1 except 0)", "group": "Ungrouped variables", "name": "a"}, "y2": {"templateType": "anything", "description": "", "definition": "a*((x2+hshift)^3+(x2+hshift)+vshift)", "group": "Ungrouped variables", "name": "y2"}, "x2": {"templateType": "anything", "description": "", "definition": "random(-1..1 except x1)", "group": "Ungrouped variables", "name": "x2"}, "hshift": {"templateType": "anything", "description": "

Random amount of horizontal shift to create variability.

", "definition": "random(-2..2)", "group": "Ungrouped variables", "name": "hshift"}, "y1": {"templateType": "anything", "description": "", "definition": "a*((x1+hshift)^3+(x1+hshift)+vshift)", "group": "Ungrouped variables", "name": "y1"}}, "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/"}]}