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Question 14 (Multiple Choice Worth 5 points)
(01.07 MC)

Simplify the expression: [tex]$(3-7i)(2-5i)$[/tex]

A. [tex]$38-34i$[/tex]

B. [tex][tex]$-29-29i$[/tex][/tex]

C. [tex]$38+29i$[/tex]

D. [tex]$-29-34i$[/tex]


Sagot :

Sure! Let's simplify the expression [tex]\((3 - 7i)(2 - 5i)\)[/tex] step-by-step using the distributive property, often known as the FOIL (First, Outer, Inner, Last) method for binomials.

Given: [tex]\( (3 - 7i)(2 - 5i) \)[/tex]

Breaking it down using FOIL:

1. First (F): Multiply the first terms in each binomial:
[tex]\[ 3 \cdot 2 = 6 \][/tex]

2. Outer (O): Multiply the outer terms in the product:
[tex]\[ 3 \cdot (-5i) = -15i \][/tex]

3. Inner (I): Multiply the inner terms in the product:
[tex]\[ (-7i) \cdot 2 = -14i \][/tex]

4. Last (L): Multiply the last terms in each binomial:
[tex]\[ (-7i) \cdot (-5i) = 35i^2 \][/tex]

Combine all these results:
[tex]\[ 6 - 15i - 14i + 35i^2 \][/tex]

Next, remember that [tex]\(i^2 = -1\)[/tex], so we substitute [tex]\(i^2\)[/tex] with [tex]\(-1\)[/tex]:
[tex]\[ 35i^2 = 35(-1) = -35 \][/tex]

Now, our expression becomes:
[tex]\[ 6 - 15i - 14i - 35 \][/tex]

Combine the like terms (real parts and imaginary parts separately):
Real part: [tex]\(6 - 35 = -29\)[/tex]
Imaginary part: [tex]\(-15i - 14i = -29i\)[/tex]

So, the expression simplifies to:
[tex]\[ -29 - 29i \][/tex]

Thus, the correct choice is:
[tex]\(-29 - 29i\)[/tex]

So, the answer is:
[tex]\[ \boxed{-29 - 29i} \][/tex]