Four complex numbers lie at the vertices of a square in the complex plane. Three of the numbers are 1 + 2i, -2 + i and -1 – 2i. What is the fourth
number?

Look, when you want to do something like put it like x^2. x2 could mean x² or x₂. so to clear confusion, know the notation. to find the product multiply the x's and you get -8x and the y's and you get 6y. since it's all being multiplied it is just -8x6y, or answer a. although the better answer is -48xy(combining -8 and 6) because you should multiply constants whenever you can.