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Simplify the expression: [tex]\((1-5i)(3+7i)\)[/tex]

A. [tex]\(38+8i\)[/tex]
B. [tex]\(-32+8i\)[/tex]
C. [tex]\(38-8i\)[/tex]
D. [tex]\(-32-8i\)[/tex]

Sagot :

Certainly! Let's simplify the expression [tex]\((1 - 5i)(3 + 7i)\)[/tex].

We use the distributive property (also known as the FOIL method for binomials):

[tex]\[ (1 - 5i)(3 + 7i) = 1 \cdot 3 + 1 \cdot 7i + (-5i) \cdot 3 + (-5i) \cdot 7i \][/tex]

Let's calculate each term separately:

1. The product of the real parts:
[tex]\[ 1 \cdot 3 = 3 \][/tex]

2. The product of the real part of the first complex number and the imaginary part of the second:
[tex]\[ 1 \cdot 7i = 7i \][/tex]

3. The product of the imaginary part of the first complex number and the real part of the second:
[tex]\[ -5i \cdot 3 = -15i \][/tex]

4. The product of the imaginary parts:
[tex]\[ -5i \cdot 7i = -35i^2 \][/tex]

Recall that [tex]\(i^2 = -1\)[/tex]. Therefore:
[tex]\[ -35i^2 = -35 \cdot (-1) = 35 \][/tex]

Now, let's combine all the calculated parts:
[tex]\[ 3 + 7i - 15i + 35 \][/tex]

Combine the real parts (3 and 35):
[tex]\[ 3 + 35 = 38 \][/tex]

Combine the imaginary parts (7i and -15i):
[tex]\[ 7i - 15i = -8i \][/tex]

Thus, the simplified expression is:
[tex]\[ 38 - 8i \][/tex]

So the correct answer is [tex]\(38 - 8i\)[/tex].

The choice corresponds to:
[tex]\[ \boxed{38 - 8i} \][/tex]