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Current time:0:00Total duration:1:13

- [Tutor] What is the sum
of the complex numbers 1 + 2i and 5 - 7i, where i is equal to
the square root of - 1. Pause this video and
see if you can figure. All right, now let's do this together. And the main realization
when you are adding or subtracting complex numbers, is to recognize that you can
get your sum or difference by adding or subtracting the real parts and then separately adding or
subtracting the complex parts. So, one way to think about it. Let me just rewrite these numbers 1 + 2i and then + 5 - 7i. We could rewrite this as 1 + 5. So, let me write that 1 + 5 that's the real part, plus we see 2i - 7i, + 2i - 7i, and so what's that going to get us? Well, we have six and then we have + 2i - 7i that is - 5i. So, plus - 5i is the same thing we can just subtract 5i right over here. So, 6 - 5i, which is choice C.