Answer:
See image
Step-by-step explanation:
These are "complex numbers" because they have the imaginary number, i, in the expression.
The 9 (and the -9) is the real part and the 3i is the imaginary part. But when you add or subtract, multiply or divide them you can manipulate them just as if the i was a variable (like x or n or y) If you learned to multiply
(x+2)(x+5)
= x^2 + 7x + 10
This problem will work the same way. You may have learned "FOIL" or using a box to multiply two binomials (two-piece things like x+2)
**SUPER IMPORTANT NOTE: i^2 is equal to -1
These particular complex numbers are called conjugates which means they have the same 'pieces' the 9 and the 3i, with only one sign different. So there is a short cut for this problem and the imaginary number falls out and we get a real number answer. This doesn't happen for every question, only when you multiply conjugates, but the method shown here works for multiplying complex numbers all the time.
