ACT Preparation / Unit 7 ACT 0616 short lesson, about 20 seconds
Adding and Multiplying Complex Numbers
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The idea
A complex number is a + bi. Add by combining real parts and imaginary parts; multiply by distributing, then replace i² with −1.
In practice
(2 + i)(3 − 4i) = 6 − 8i + 3i − 4i² = 6 − 5i + 4 = 10 − 5i.
Where people slip
The i² term turns real and joins the real part.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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