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14 May, 10:11

If x+yi/i = 8 + 10i, where x and y are real, what is the value of (x + yi) (x - yi) ?

A 164

B 150

C. 75

D. 100

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Answers (2)
  1. 14 May, 12:42
    0
    A. 164

    Step-by-step explanation:

    (x+yi) (x-yi) - > (8+10i) (8-10i)

    rule: * (a-b) (a+b) = a^2+b^2

    (8+10i) (8-10i) = 64-100i^2

    rule: i^2 = (-1)

    64-100i^2 = 64-100 (-1)

    =64+100

    =164
  2. 14 May, 13:57
    0
    164

    Step-by-step explanation:

    (x + iy) / i = 8 + 10i

    (x + iy) = (8 + 10i) (i) = 8i + 10i²

    = - 10 + 8i

    (-10 + 8i) (-10 - 8i) = (-10) ² + 8² = 164
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