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Elementary examples of multiplication and addition of complex numbers. Four parts.

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Original: https://numbas.mathcentre.ac.uk/question/11784/arithmetics-of-complex-numbers-i/ by Newcastle University Mathematics ans Statistics

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Translated to German.

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Schreiben Sie die folgenden komplexenz Zahlen in der Form $a+bi\\;$ mit $a$ und $b$ in $\\mathbb R$.

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Schreiben Sie $a$ und $b$ als Bruchzahlen oder als ganze Zahlen.

", "advice": "

a)

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Die Multiplikationsformel für komplexe Zahlen ist
\\[ (a+bi)(c+di) = (ac-bd) + (ad+bc)i \\]

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Also gilt
\\[ \\simplify[timesdot]{{a}*{b}} = (\\simplify[timesdot]{{Re(a)}*{Re(b)} - {Im( a)}*{Im(b)}}) + (\\simplify[timesdot]{{Re(a)}*{Im(b)} + {Im( a)}*{Re(b)}})i \\]
Die Lösung ist also

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\\[(\\simplify[std]{{a}})(\\simplify[std]{{b}})=\\var{a*b}\\]

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b)

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Wir schreiben die zweite Potenz aus als

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$(\\simplify[std]{{a1}})^2= (\\simplify[std]{{a1}}) (\\simplify[std]{{a1}})$ und berechnen das Produkt:

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\\[\\begin{eqnarray*}(\\simplify[std]{{a1}})^2&=& (\\simplify[std]{{a1}}) (\\simplify[std]{{a1}})\\\\ &=& \\simplify[timesdot]{({Re(a1)}*{Re(a1)} - {Im(a1)}*{Im(a1)})+ ({Re(a1)}*{Im(a1)} + {Im(a1)}*{Re(a1)})i}\\\\ &=& \\simplify[std,timesdot]{{a1^2}} \\end{eqnarray*} \\]

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c)

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Es gilt $i^2=-1$, also $i^3=i^2i=-i$.

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Somit:
\\[ \\begin{eqnarray*} \\simplify[std,!otherNumbers]{{a3} + {b3} * i + {c3} * i ^ 2 + {d3} * i ^ 3}&=&\\simplify[std]{{a3} + {b3} * i -{c3} -({d3} * i)}\\\\ &=&\\simplify[std]{ {a3} -{c3} + ({b3} -{d3}) * i}\\\\ &=&\\simplify[std]{{a3 -c3} + {b3 -d3} * i} \\end{eqnarray*} \\]

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d)

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Wir multiplizieren die Zahlen in zwei Schritten und erhalten:
\\[ \\begin{eqnarray*} (\\var{z1})(\\var{z2})(\\var{z3})&=&((\\var{z1})(\\var{z2}))(\\var{z3})\\\\ &=&(\\var{z1*z2})(\\var{z3})\\\\ &=&\\var{z1*z2*z3} \\end{eqnarray*} \\]

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$(\\simplify[std]{{a}})(\\simplify[std]{{b}})\\;=\\;$[[0]].

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$(\\simplify[std]{{a1}})^2\\;=\\;$[[0]].

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Schreiben Sie Ihre Antworten als Bruchzahlen oder ganze Zahlen.

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$\\simplify[std,!otherNumbers]{{a3} + {b3} * i + {c3} * i ^ 2 + {d3} * i ^ 3}\\;=\\;$[[0]].

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Schreiben Sie Ihre Antworten als Bruchzahlen oder als ganze Zahlen.

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$(\\simplify[std]{{z1}}) (\\simplify[std]{{z2}}) (\\simplify[std]{{z3}})\\;=\\;$[[0]].

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Schreiben Sie Ihre Antworten als Bruchzahlen oder als ganze Zahlen.

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