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shibble21
17.12.2020 •
Mathematics
29. Which of the following expressions will result in a real answer after being simplified? Select all that apply.
A. (4+5i)(4-5i)
B. (4+91)(41-9)
C. (3+2i)(3-2i)
D. (2i+5i) (21-3)
E. (312+7i) (312-7i)
F. (3i2+7i)(312+7i)
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Ответ:
A, B, C, and E
Step-by-step explanation:
If both sides are real numbers, then the product will be a real number.
If in at least one of the sides we have a complex number, then the product will be real if:
The other number is zero.
The other number is the conjugate of the first.
This is when:
Suppose we have a number:
z = a + b*i
The conjugate will be:
w = a - b*i
And the product between them is:
(a + b*i)*(a - b*i) = a^2 + a*b*i - a*b*i + b^2 = a^2 + b^2
Then the options that will have a real answer are:
A. (4+5i)(4-5i) = 4^2 + 5^2 = 16 + 25 = 41
B. (4 + 91)*(41 - 9) = 3040
C. (3 + 2*i)*(3 -2*i) = 3^2 + 2^2 = 9 + 4 = 13
E. (312 + 7i)*(312 - 7i) = 312^2 + 7^2 = 97,393
Ответ:
you get n times the second number.
Step-by-step explanation: example: 5x9.
5 sets of 9 is 9+9+9+9+9=45