Which of the following statements are true about the simplified form of the expression (2 + 2i) / (1 - I)? Select all that apply.

The simplified form is 2i
The simplified form is 4i
The simplified form is 2 + 2i
The simplified form is 4 + 4i
The simplified form is a complex number because complex numbers are closed under division.
The simplified form is not a complex number because complex numbers are not closed under division.

1 answer

To simplify the expression \((2 + 2i) / (1 - i)\), we can multiply the numerator and the denominator by the conjugate of the denominator, which is \(1 + i\).

So, we have:

\[ \frac{(2 + 2i)(1 + i)}{(1 - i)(1 + i)} \]

Calculating the denominator:

\[ (1 - i)(1 + i) = 1^2 - i^2 = 1 - (-1) = 2 \]

Now, calculating the numerator:

\[ (2 + 2i)(1 + i) = 2(1) + 2(i) + 2i(1) + 2i(i) = 2 + 2i + 2i - 2 = 2 + 4i - 2 = 4i \]

So, combining the results, we have:

\[ \frac{4i}{2} = 2i \]

Now let's analyze the statements:

  1. The simplified form is 2i - True (This is what we found)
  2. The simplified form is 4i - False (We found it to be 2i)
  3. The simplified form is 2 + 2i - False (We found it to be 2i)
  4. The simplified form is 4 + 4i - False (We found it to be 2i)
  5. The simplified form is a complex number because complex numbers are closed under division. - True (The result is indeed a complex number)
  6. The simplified form is not a complex number because complex numbers are not closed under division. - False (That statement is incorrect; complex numbers are closed under division, except when dividing by zero)

In conclusion, the true statements are:

  • The simplified form is 2i.
  • The simplified form is a complex number because complex numbers are closed under division.