SAT and ACT math terms · SAT Math, ACT Math
Complex number
Complex number: A number of the form a + bi, where a and b are real numbers and i² = −1.
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What it means
Complex numbers are added by combining real and imaginary parts and multiplied using the distributive property and i² = −1. Powers of i repeat in a cycle of four: i, −1, −i, 1.
Quadratic equations with a negative discriminant have complex solutions.
Example
(3 + 2i)(1 − i) = 3 − 3i + 2i − 2i² = 3 − i + 2 = 5 − i.
On the exam
The ACT includes complex numbers in its number and quantity questions.