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What is the value of this expression?

[tex] (5 + 3i) - (5 + 3i)(5 - 5i) [/tex]

A. [tex][tex]$-5 - 37i$[/tex][/tex]
B. [tex][tex]$-35 + 13i$[/tex][/tex]
C. [tex][tex]$35 - 13i$[/tex][/tex]
D. [tex][tex]$-5 + 37i$[/tex][/tex]

Sagot :

To solve the given expression [tex]\((5 + 3i) - (5 + 3i)(5 - 5i)\)[/tex], we will break it down step-by-step.

First, let's define the complex numbers involved:
- [tex]\( z_1 = 5 + 3i \)[/tex]
- [tex]\( z_2 = 5 - 5i \)[/tex]

### Step 1: Calculate the first term, which is simply [tex]\( z_1 \)[/tex]:
[tex]\[ z_1 = 5 + 3i \][/tex]

### Step 2: Calculate the product of [tex]\( z_1 \)[/tex] and [tex]\( z_2 \)[/tex]:
[tex]\[ z_1 \cdot z_2 = (5 + 3i)(5 - 5i) \][/tex]

To perform this multiplication, we apply the distributive property (FOIL method):
[tex]\[ (5 + 3i)(5 - 5i) = 5 \cdot 5 + 5 \cdot (-5i) + 3i \cdot 5 + 3i \cdot -5i \][/tex]

Simplifying each term:
[tex]\[ = 25 - 25i + 15i - 15i^2 \][/tex]

Since [tex]\( i^2 = -1 \)[/tex]:
[tex]\[ -15i^2 = -15(-1) = 15 \][/tex]

Now, simplifying further:
[tex]\[ 25 - 25i + 15i + 15 \][/tex]
Combine the real and imaginary parts:
[tex]\[ (25 + 15) + (-25i + 15i) = 40 - 10i \][/tex]

So, the result of [tex]\( z_1 \cdot z_2 \)[/tex] is:
[tex]\[ 40 - 10i \][/tex]

### Step 3: Calculate the value of the expression:
[tex]\[ (5 + 3i) - (40 - 10i) \][/tex]

Subtract the corresponding real parts and imaginary parts separately:
[tex]\[ = (5 - 40) + (3i - (-10i)) \][/tex]
[tex]\[ = -35 + 13i \][/tex]

Thus, the value of the expression [tex]\((5 + 3i) - (5 + 3i)(5 - 5i)\)[/tex] is:
[tex]\[ -35 + 13i \][/tex]

Therefore, the correct answer is:
[tex]\[ \boxed{-35 + 13i} \][/tex]

Option B matches this result. So, the correct answer is:
B. [tex]\(-35 + 13i\)[/tex]