Question

the imaginary unit is represented by the symbol.
a complex number is written in the form.
the is used to expand expressions of the form $(a + b)^n$.
the coefficients in the binomial expansion can be found using.
in the expression $a+bi$, $a$ is the part.

Explanation:

Step1: Recall imaginary unit symbol

The imaginary unit is represented by $i$.

Step2: Recall complex - number form

A complex number is written in the form $a + bi$, where $a$ and $b$ are real numbers.

Step3: Recall binomial - expansion formula

The binomial theorem is used to expand expressions of the form $(a + b)^n$.

Step4: Recall binomial - coefficient method

The coefficients in the binomial expansion can be found using Pascal's triangle or the combination formula $C(n,k)=\frac{n!}{k!(n - k)!}$.

Step5: Recall parts of complex number

In the expression $a+bi$, $a$ is the real part.

Answer:

1. $i$
2. $a + bi$
3. Binomial theorem
4. Pascal's triangle (or combination formula)
5. Real