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Let $a$ and $b$ be complex numbers. If $a + b = 1$ and $a^2 + b^2 = 2,$ then what is $a^3 + b^3?$

 Aug 14, 2024
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Let's give this problem a shot. 

Now, we know that (a+b)2=a2+2ab+b2

 

From the problem, we ALSO know that (a+b)2=12=1

Thus, we have the equation a2+2ab+b2=1

Since the problem gives us the value of a2+b2=2, we can easily figure out what ab is. 

We have

2ab+2=12ab=1ab=1/2

 

The value of ab will come in handy later. 

 

Now, let's focus on what we must find. a^3+b^3. From a handy equation, we know that

a3+b3=(a+b)(a2ab+b2)

 

Wait! We already know all the values needed to solve the problem. Plugging in 1, 2, and -1/2, we get

a3+b2=(1)(2(1/2))=2+1/2=5/2

 

Thus, our final answer is 5/2. 

 

Thanks! :)

 Aug 15, 2024
edited by NotThatSmart  Aug 15, 2024

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