yes it does
they use numbers not words.
Complex numbers are the square roots of negative numbers. i.e. root -1 = i
You can use computers or other digital equipment. OR You can use numbers and do arithmetic.
computers, calculators
electrical engineers and quantum mechanics use them.
Yes, many
I suggest you read the Wikipedia article con complex numbers, specifically the section "Applications". One example is electrical engineering: in the case of AC, it helps to express all voltages, currents and impedances (equivalent of resistances) as complex numbers.
I'm not sure about how to use complex numbers to do this, but I've posted a link to a pretty neat website about Synthetic Division.
using contraction and expansion
when you multiply it with another polynomial
Computers use binary numbers. This is ones and zeros.
It shows multiple numbers in order to use in addition, subtraction, etc.