Let $a$ and $b$ be complex numbers. If $a + b = 1$ and $a^2 + b^2 = 2,$ then what is $a^3 + b^3?$
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)(a2−ab+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! :)