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Compute the absolute values of given complex numbers

For each of the following complex numbers, compute the absolute value.

  1. 1+i.
  2. 3 + 4i.
  3. \frac{1+i}{1-i}.
  4. 1+i+i^2.
  5. i^7 + i^{10}.
  6. 2(1-i) + 3(2+i).

  1. Using the formula for the absolute value of a complex number we compute,

        \[ |1+i| = \sqrt{1^2 + 1^2} = \sqrt{2}. \]

  2. Using the formula for the absolute value of a complex number we compute,

        \[ |3+4i| = \sqrt{3^2 + 4^2} = \sqrt{25} = 5. \]

  3. Using the fact that \left| \frac{z_1}{z_2} \right| = \frac{|z_1|}{|z_2|} and the formula for the absolute value of a complex number we have,

        \[ \left| \frac{1+i}{1-i} \right| = \frac{|1+i|}{|1-i|} = \frac{\sqrt{2}}{\sqrt{2}} = 1. \]

  4. Using i^2 = -1 and the formula for the absolute value of a complex number we have

        \[ |1 + i + i^2| = |i| = \sqrt{1^2} = 1. \]

  5. Using that i^4 = 1 we have

        \[ |i^7 + i^{10}| = |i^3 + i^2| = |-1 - i| = \sqrt{(-1)^2 + (-1)^2} = \sqrt{2}. \]

  6. We compute,

        \[ |2(1-i) + 3(2+i)| = |2 - 2i + 6 + 3i| = |8 + i| = \sqrt{8^2 + 1^2} = \sqrt{65}. \]

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