20% of what original number is 25?
1 answer:
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Answer:
D. 13
Step-by-step explanation:
You can do the product in the straight-forward way ...
... (3 -2i)(3 +2i) = 3·3 +3·2i -3i·3 -(2i)(2i)
... = 9 +6i -6i -4i² . . . . . note the middle two terms cancel
Recognize that i = √-1, so i² = -1. Then the sum is
... = 9 -4(-1) = 9+4 = 13
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Your graphing calculator can do this product, too.
