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Which expression is equivalent to [tex]$(4+7i)(3+4i)$[/tex]?

A. [tex]-16 + 37i[/tex]
B. [tex]12 - 28i[/tex]
C. [tex]16 - 37i[/tex]
D. [tex]37 + 16i[/tex]


Sagot :

To determine which expression is equivalent to [tex]\((4 + 7i)(3 + 4i)\)[/tex], let's go through the multiplication of these two complex numbers step by step.

To multiply two complex numbers, we can use the distributive property (also known as the FOIL method for binomials):

[tex]\[ (4 + 7i)(3 + 4i) \][/tex]

Step 1: Distribute [tex]\(4\)[/tex] in the first term over the second complex number:
[tex]\[ 4 \cdot 3 + 4 \cdot 4i = 12 + 16i \][/tex]

Step 2: Distribute [tex]\(7i\)[/tex] in the first term over the second complex number:
[tex]\[ 7i \cdot 3 + 7i \cdot 4i = 21i + 28i^2 \][/tex]

Step 3: Combine the results:
[tex]\[ 12 + 16i + 21i + 28i^2 \][/tex]

Step 4: Recall that [tex]\(i^2 = -1\)[/tex], so substitute [tex]\(-1\)[/tex] in for [tex]\(i^2\)[/tex]:
[tex]\[ 12 + 16i + 21i + 28(-1) \][/tex]

Step 5: Simplify the expression:
[tex]\[ 12 + 16i + 21i - 28 \][/tex]

Step 6: Combine like terms (real parts together and imaginary parts together):
[tex]\[ (12 - 28) + (16i + 21i) = -16 + 37i \][/tex]

Therefore, the expression that is equivalent to [tex]\((4 + 7i)(3 + 4i)\)[/tex] is:

[tex]\[ -16 + 37i \][/tex]

So, the correct option is:
[tex]\[ -16 + 37i \][/tex]