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If i = sqrt-1 then 4 + 5 ( - (1)/(2) + ...

If `i = sqrt-1 ` then `4 + 5 ( - (1)/(2) + (i sqrt3)/( 2)) ^( 334) + 3 (- (1)/(2) + ( i sqrt3)/( 2))^365` is equal to to

A

`1- i sqrt3`

B

`-1 + sqrt3`

C

`i sqrt3`

D

`-i sqrt3`

Text Solution

AI Generated Solution

The correct Answer is:
To solve the expression \( 4 + 5 \left( -\frac{1}{2} + \frac{i \sqrt{3}}{2} \right)^{334} + 3 \left( -\frac{1}{2} + \frac{i \sqrt{3}}{2} \right)^{365} \), we will use the concept of cube roots of unity. ### Step-by-Step Solution: 1. **Identify the complex number**: Let \( \omega = -\frac{1}{2} + \frac{i \sqrt{3}}{2} \). This is one of the cube roots of unity, specifically \( \omega = e^{2\pi i / 3} \). 2. **Properties of cube roots of unity**: The cube roots of unity satisfy the equation \( \omega^3 = 1 \) and \( 1 + \omega + \omega^2 = 0 \). 3. **Calculate powers of \( \omega \)**: - Since \( \omega^3 = 1 \), we can reduce the exponents modulo 3: - \( 334 \mod 3 = 1 \) (since \( 334 = 3 \times 111 + 1 \)) - \( 365 \mod 3 = 2 \) (since \( 365 = 3 \times 121 + 2 \)) 4. **Substitute back into the expression**: \[ 4 + 5 \omega^{334} + 3 \omega^{365} = 4 + 5 \omega^1 + 3 \omega^2 \] This simplifies to: \[ 4 + 5 \omega + 3 \omega^2 \] 5. **Use the identity \( 1 + \omega + \omega^2 = 0 \)**: From this identity, we can express \( \omega^2 \) in terms of \( \omega \): \[ \omega^2 = -1 - \omega \] Substitute this into the expression: \[ 4 + 5 \omega + 3(-1 - \omega) = 4 + 5 \omega - 3 - 3 \omega \] This simplifies to: \[ 4 - 3 + (5 - 3) \omega = 1 + 2 \omega \] 6. **Substituting the value of \( \omega \)**: Now substitute \( \omega = -\frac{1}{2} + \frac{i \sqrt{3}}{2} \): \[ 1 + 2\left(-\frac{1}{2} + \frac{i \sqrt{3}}{2}\right) = 1 - 1 + i \sqrt{3} = i \sqrt{3} \] ### Final Result: Thus, the value of the expression is: \[ \boxed{i \sqrt{3}} \]
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