How to Solve a^2011 for a Complex Number Satisfying a^2-a+1=0?

In summary, to find the value of a^2011 when given the equation a^2-a+1=0, one must first solve for 'a' using the quadratic formula. Then, convert the resulting complex number into cis notation and apply De Moivre's theorem to find a^2011. Another method is to find the factorization of a^3+1 and use that to simplify the expression for a^2011.
  • #1
sankarshana016
6
0
If a is a complex number, and a^2-a+1=0, then a^2011=?

I tried using De Moivre's theorem, Taking a=cosθ+isinθ, but didn't get anywhere, got stuck at
cos2θ+isin2θ-cosθ-isinθ+1=0. What do I do?
 
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  • #2
First you should solve the equation for 'a'. After that, you can calculate the argumentum and the abs. value of 'a', resulting in a = r*(cos(theta) + i* sin(theta)). Finally, apply De Moivre for calculating a^2011.
 
  • #3
sankarshana016 said:
Taking a=cosθ+isinθ, but didn't get anywhere

a=cosθ+isinθ assumes that |a| = 1. That is wrong unless you already know that |a| = 1.

You can just solve the quadratic equation for a (using the standard formula) to get the real and imaginary parts.
 
  • #4
sankarshana016 said:
If a is a complex number, and a^2-a+1=0, then a^2011=?

I tried using De Moivre's theorem, Taking a=cosθ+isinθ, but didn't get anywhere, got stuck at
cos2θ+isin2θ-cosθ-isinθ+1=0. What do I do?
Do you know the factorization of ##\ a^3+1\ ?##
 
  • #5
SammyS said:
Do you know the factorization of ##\ a^3+1\ ?##

It might be difficult to guess that clever trick. Here's another way. You know a^2=a-1. Can you find a simple expression for a^3?
 
  • #6
sankarshana016 said:
If a is a complex number, and a^2-a+1=0, then a^2011=?

I tried using De Moivre's theorem, Taking a=cosθ+isinθ, but didn't get anywhere, got stuck at
cos2θ+isin2θ-cosθ-isinθ+1=0. What do I do?

Dude, first find the complex number "a" by using quadratic formula. Then you convert it to "cis" notation, and then you finally apply De Moivre's theorem.
 
  • #7
##a^{2011}=a^{6\cdot 335+1}=(a^6)^{335}a##
What is ##a^6##?
 

1. What are complex numbers?

Complex numbers are numbers that consist of both a real and an imaginary part. They are written in the form a + bi, where a is the real part and bi is the imaginary part, with i being the imaginary unit equal to the square root of -1.

2. How are complex numbers used in mathematics?

Complex numbers are used in many areas of mathematics, including algebra, geometry, and calculus. They are particularly useful in solving problems involving electrical circuits, quantum mechanics, and fluid dynamics.

3. What is the difference between a real number and a complex number?

A real number is any number that can be represented on the number line, including all positive and negative integers, fractions, and decimals. A complex number, on the other hand, includes both a real and imaginary part and cannot be represented on a number line.

4. How do you add and subtract complex numbers?

To add or subtract complex numbers, you simply combine the real parts and the imaginary parts separately. For example, to add (3 + 2i) and (5 - 4i), you add 3 and 5 to get 8, and add 2i and -4i to get -2i, giving you a final answer of 8 - 2i.

5. Can complex numbers have exponents?

Yes, complex numbers can have exponents. To raise a complex number to a power, you can use the expression (a + bi)^n = (a^n + nb^(n-1)i + ... + nbi^(n-1)). This is known as de Moivre's formula.

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