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Which complex number is equivalent to the given expression?

[tex]\[ (-45 - 22i) + 2(5 - 3i)(5 + 3i) \][/tex]

A. [tex][tex]$-11 + 22i$[/tex][/tex]
B. [tex][tex]$23 - 22i$[/tex][/tex]
C. [tex][tex]$-13 + 38i$[/tex][/tex]
D. [tex][tex]$-30 - 25i$[/tex][/tex]

Sagot :

To determine which complex number is equivalent to the given expression, follow these steps:

1. Identify the given expression:
[tex]\[ (-45 - 22i) + 2(5 - 3i)(5 + 3i) \][/tex]

2. Simplify the expression inside the parentheses:
Start by calculating [tex]\((5 - 3i)(5 + 3i)\)[/tex]. Recognize that this is a product of conjugates. The formula for the product of conjugates is:
[tex]\[ (a - bi)(a + bi) = a^2 + b^2 \][/tex]
Here, [tex]\(a = 5\)[/tex] and [tex]\(b = 3\)[/tex]:
[tex]\[ (5 - 3i)(5 + 3i) = 5^2 + 3^2 = 25 + 9 = 34 \][/tex]
So:
[tex]\[ (5 - 3i)(5 + 3i) = 34 \][/tex]

3. Multiply the result by 2:
[tex]\[ 2 \times 34 = 68 \][/tex]

4. Add to the initial complex number [tex]\((-45 - 22i)\)[/tex]:
[tex]\[ (-45 - 22i) + 68 \][/tex]

5. Separate the real and imaginary parts:
[tex]\[ \text{Real part: } -45 + 68 = 23 \][/tex]
[tex]\[ \text{Imaginary part : } -22i \text{ remains.} \][/tex]

6. Combine these to form the final complex number:
[tex]\[ 23 - 22i \][/tex]

Thus, the complex number equivalent to the given expression is:
[tex]\[ \boxed{23 - 22i} \][/tex]
So the correct answer is:
B. [tex]\(23 - 22i\)[/tex]
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