SATMathematics Practice Test 1

To calculate $\left(7+3\mathit{i}\right)+\left(-8+9\mathit{i}\right)$,add the real parts of each complex number, $7+\left(-8\right)=-1$,and then add the imaginary parts, $3\mathit{i}+9\mathit{i}=12\mathit{i}$.
The result is $-1+12\mathit{i}.$
Choices B, C, and D are incorrect and likely result from common errors that arise when adding complex numbers.
For example, choice B is the result of adding 3i and −9i, and choice C is the result of adding 7 and 8.