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All that is required in this question is to substitute $z=x+iy$ into the expression for $f(z)$, and rearrange to the form $f(z)=g(x,y)+ih(x,y)$, hence

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\\[\\begin{align}f(z)&=f(x+iy)\\\\&=\\simplify{{a1}*(x+iy)^{n}-i*{b1}*(x+iy)^{n-1}}\\\\&=\\simplify{{n2}*({a1}*(x^2-y^2)+{b1}*y) + {n3}*({a1}*(x^3-3*x*y^2)+{2*b1}*x*y)+i*({n2}*({2*a1}*x*y-{b1}*x)+{n3}*({3*a1}*x^2*y-{a1}*y^3-{b1}*(x^2+y^2)))}.\\end{align}\\]

", "name": "Hollie's copy of Function in real-imaginary form", "variablesTest": {"maxRuns": 100, "condition": ""}, "parts": [{"gaps": [{"answer": "{n2}*({a1}*(x^2-y^2)+{b1}*y) + {n3}*({a1}*(x^3-3*x*y^2)+{2*b1}*x*y)", "showCorrectAnswer": true, "showpreview": true, "expectedvariablenames": ["x", "y"], "type": "jme", "checkingtype": "absdiff", "answersimplification": "std", "marks": 1, "vsetrange": [0, 1], "checkingaccuracy": 0.001, "checkvariablenames": true, "vsetrangepoints": 5, "scripts": {}}, {"answer": "{n2}*({2*a1}*x*y-{b1}*x)+{n3}*({3*a1}*x^2*y-{a1}*y^3-{b1}*(x^2-y^2))", "showCorrectAnswer": true, "showpreview": true, "expectedvariablenames": ["x", "y"], "type": "jme", "checkingtype": "absdiff", "answersimplification": "std", "marks": 1, "vsetrange": [0, 1], "checkingaccuracy": 0.001, "checkvariablenames": true, "vsetrangepoints": 5, "scripts": {}}], "showCorrectAnswer": true, "prompt": "

$g(x,y)=$ [[0]].

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$h(x,y)=$ [[1]].

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Express $f(z)$ in real-imaginary form, given that $z=x+iy$.

", "notes": "

15/7/2012:

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Added tags.

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25/02/2014

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Enable unexpected variable names. AJY

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17/02/2014

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Fix typo in solution to $h(x,y)$. AJY

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Express the function $f(z)=\\simplify{{a1}*z^{n}-i*{b1}*z^{n-1}}$ in real-imaginary form $f(z)=g(x,y)+ih(x,y)$, given that $z=x+iy$.

", "contributors": [{"name": "Hollie Tarr", "profile_url": "https://numbas.mathcentre.ac.uk/accounts/profile/1176/"}]}]}], "contributors": [{"name": "Hollie Tarr", "profile_url": "https://numbas.mathcentre.ac.uk/accounts/profile/1176/"}]}