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Simplify the following and leave your answer in standard form: (1-i)6 x (sqrt(3)cis(-30^))42i-1

Mathematics

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Here's the solution for Question 1.2.

Question 1.2

Simplify the following and leave your answer in standard form:

(1−i)6×(3cis(−30∘))42i−1\frac{(1-i)^6 \times (\sqrt{3}\text{cis}(-30^\circ))^4}{2i-1}
  1. Convert (1−i)(1-i) to polar form and calculate (1−i)6(1-i)^6.

    First, convert 1−i1-i to polar form r(cos⁡θ+isin⁡θ)r(\cos\theta + i\sin\theta).
    The modulus is r=12+(−1)2=1+1=2r = \sqrt{1^2 + (-1)^2} = \sqrt{1+1} = \sqrt{2}.
    The argument is θ=arctan⁡(−11)=−45∘\theta = \arctan\left(\frac{-1}{1}\right) = -45^\circ (since 1−i1-i is in the fourth quadrant).
    So, 1−i=2cis(−45∘)1-i = \sqrt{2}\text{cis}(-45^\circ).

    Now, use De Moivre's Theorem to calculate (1−i)6(1-i)^6:

    (1−i)6=(2cis(−45∘))6(1-i)^6 = (\sqrt{2}\text{cis}(-45^\circ))^6 =(2)6cis(6×−45∘)= (\sqrt{2})^6 \text{cis}(6 \times -45^\circ) =23cis(−270∘)= 2^3 \text{cis}(-270^\circ) =8cis(−270∘)= 8 \text{cis}(-270^\circ)

    Since −270∘-270^\circ is equivalent to 90∘90^\circ (i.e., −270∘+360∘=90∘-270^\circ + 360^\circ = 90^\circ):

    =8cis(90∘)= 8 \text{cis}(90^\circ)

    Convert back to rectangular form:

    =8(cos⁡90∘+isin⁡90∘)= 8(\cos 90^\circ + i\sin 90^\circ) =8(0+i(1))= 8(0 + i(1)) =8i= 8i
  2. Calculate (3cis(−30∘))4(\sqrt{3}\text{cis}(-30^\circ))^4.

    Use De Moivre's Theorem:

    (3cis(−30∘))4=(3)4cis(4×−30∘)(\sqrt{3}\text{cis}(-30^\circ))^4 = (\sqrt{3})^4 \text{cis}(4 \times -30^\circ) =9cis(−120∘)= 9 \text{cis}(-120^\circ)

    Convert to rectangular form:

    =9(cos⁡(−120∘)+isin⁡(−120∘))= 9(\cos(-120^\circ) + i\sin(-120^\circ)) =9(−12−i32)= 9\left(-\frac{1}{2} - i\frac{\sqrt{3}}{2}\right) =−92−i932= -\frac{9}{2} - i\frac{9\sqrt{3}}{2}
  3. Multiply the results from Step 1 and Step 2 to get the numerator.

    Numerator =(8i)×(−92−i932)= (8i) \times \left(-\frac{9}{2} - i\frac{9\sqrt{3}}{2}\right)

    =8i(−92)+8i(−i932)= 8i\left(-\frac{9}{2}\right) + 8i\left(-i\frac{9\sqrt{3}}{2}\right) =−36i−i27232= -36i - i^2 \frac{72\sqrt{3}}{2}

    Since i2=−1i^2 = -1:

    =−36i−(−1)(363)= -36i - (-1)(36\sqrt{3}) =363−36i= 36\sqrt{3} - 36i
  4. Simplify the denominator.

    The denominator is 2i−12i-1, which can be written as −1+2i-1+2i.

  5. Divide the numerator by the denominator and express in standard form.

    363−36i−1+2i\frac{36\sqrt{3} - 36i}{-1 + 2i}

    Multiply the numerator and denominator by the conjugate of the denominator, which is −1−2i-1-2i:

    (363−36i)(−1−2i)(−1+2i)(−1−2i)\frac{(36\sqrt{3} - 36i)(-1 - 2i)}{(-1 + 2i)(-1 - 2i)}

    Calculate the denominator:

    (−1)2−(2i)2=1−4i2=1−4(−1)=1+4=5(-1)^2 - (2i)^2 = 1 - 4i^2 = 1 - 4(-1) = 1 + 4 = 5

    Calculate the numerator:

    (363−36i)(−1−2i)(36\sqrt{3} - 36i)(-1 - 2i) =363(−1)+363(−2i)−36i(−1)−36i(−2i)= 36\sqrt{3}(-1) + 36\sqrt{3}(-2i) - 36i(-1) - 36i(-2i) =−363−723i+36i+72i2= -36\sqrt{3} - 72\sqrt{3}i + 36i + 72i^2 =−363−723i+36i−72= -36\sqrt{3} - 72\sqrt{3}i + 36i - 72

    Group the real and imaginary parts:

    =(−363−72)+(36−723)i= (-36\sqrt{3} - 72) + (36 - 72\sqrt{3})i

    Now, combine the numerator and denominator:

    (−363−72)+(36−723)i5\frac{(-36\sqrt{3} - 72) + (36 - 72\sqrt{3})i}{5} =−363−725+36−7235i= \frac{-36\sqrt{3} - 72}{5} + \frac{36 - 72\sqrt{3}}{5}i

    The final answer in standard form is ∗−363−725+36−7235i\boxed*{\frac{-36\sqrt{3} - 72}{5} + \frac{36 - 72\sqrt{3}}{5}i}.

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