Mathematics

Question

What is the value of (7 + 2i)(3 - i)?

1 Answer

  • There are two ways to work this out: normal variables or using "imaginary" numbers.

    Normal variables:
    [tex] (7+2i)(3-i)\\(7*3)+[7*(-i)]+(3*2i)+[2i*(-i)]\\21-7i+6i-2i^{2}\\\\21-i-2i^{2}[/tex]

    Imaginary numbers:
    Using the result from earlier:
    [tex]21-i-2i^{2}[/tex]
    Now since [tex] i = \sqrt{-1}[/tex], then the expression becomes:
    [tex] 21-i-2i^{2}\\21-i-2(\sqrt{-1})^{2}\\21-i+(-2)(-1)\\21-i+2\\\\23-i[/tex]
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