Question

Which expression represents the number -2i(5- i) + (17- 8i) rewritten in a + bi

form?
O 15-18i
O 15-2i
O 19 - 18i
O 11 + 8i

Answer 1

(a) 15 -18i

Explanation:

You want the simplified form of the expression -2i(5- i) + (17- 8i).

Complex numbers

For many purposes, the value i in a complex number can be treated in the same way a variable would be treated. When simplifying an expression involving i, any instances of i² can be replaced with the real value -1.

-2i(5- i) + (17- 8i) = -10i +2i² +17 -8i

= -2 +17 +(-10 -8)i

= 15 -18i

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Additional comment

Your scientific or graphing calculator can probably help you evaluate such expressions.