Question

Express the complex number 3(cos270° + i sin270°) in standard a + bi form.

Answer 1

Answer is choice C
The expression given is equivalent to -3i

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Explanation:

Using a calculator, a reference sheet, or the unit circle, you'll find that:
cos(270) = 0
sin(270) = -1

So this means
z = 3(cos(270)+i*sin(270))
z = 3(0+i*(-1))
z = 3*0+3*i*(-1)
z = 0-3i
z = -3i
which is in a+bi form where a = 0 and b = -3