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Imaginary unit and complex number operations
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The imaginary unit is defined as:
Simplify: โ(-16)
Step 1: Recall that i = โ(-1): The imaginary unit i is defined as โ(-1)
Step 2: Factor out -1: โ(-16) = โ(16 ร (-1)) = โ16 ร โ(-1)
Step 3: Simplify: = 4i
Answer: 4i
Simplify:
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Therefore:
A complex number has the form:
where:
Example:
Pattern repeats every 4:
Combine like terms (real with real, imaginary with imaginary):
Use FOIL and remember :
The conjugate of is .
Property: (always real!)
Factor out :
Answer:
Add: (3 + 2i) + (5 - 4i)
Step 1: Group real and imaginary parts: (3 + 2i) + (5 - 4i) = (3 + 5) + (2i - 4i)
Step 2: Combine like terms: Real parts: 3 + 5 = 8 Imaginary parts: 2i - 4i = -2i
Step 3: Write in standard form: 8 - 2i
Answer: 8 - 2i
Add:
Combine real parts and imaginary parts separately:
Real parts: Imaginary parts:
Answer:
Multiply: (2 + 3i)(4 - i)
Step 1: Use FOIL method: First: 2 ร 4 = 8 Outer: 2 ร (-i) = -2i Inner: 3i ร 4 = 12i Last: 3i ร (-i) = -3iยฒ
Step 2: Combine: 8 - 2i + 12i - 3iยฒ
Step 3: Remember that iยฒ = -1: -3iยฒ = -3(-1) = 3
Step 4: Combine all terms: 8 - 2i + 12i + 3 = (8 + 3) + (-2i + 12i) = 11 + 10i
Answer: 11 + 10i
Divide: (6 + 8i)/(1 - i)
Step 1: Multiply by conjugate of denominator: The conjugate of (1 - i) is (1 + i)
Step 2: Multiply numerator and denominator: (6 + 8i)/(1 - i) ร (1 + i)/(1 + i)
Step 3: Expand numerator: (6 + 8i)(1 + i) = 6 + 6i + 8i + 8iยฒ = 6 + 14i + 8(-1) = 6 + 14i - 8 = -2 + 14i
Step 4: Expand denominator: (1 - i)(1 + i) = 1 + i - i - iยฒ = 1 - (-1) = 1 + 1 = 2
Step 5: Divide: (-2 + 14i)/2 = -2/2 + 14i/2 = -1 + 7i
Answer: -1 + 7i
Multiply:
Notice these are conjugates! Use the formula
Or use FOIL:
Answer: (a real number!)
Find all solutions to xยฒ + 4 = 0 in the complex number system.
Step 1: Solve for xยฒ: xยฒ = -4
Step 2: Take square root of both sides: x = ยฑโ(-4)
Step 3: Simplify โ(-4): โ(-4) = โ(4 ร (-1)) = โ4 ร โ(-1) = 2i
Step 4: Write both solutions: x = 2i or x = -2i
Step 5: Verify x = 2i: (2i)ยฒ + 4 = 4iยฒ + 4 = 4(-1) + 4 = -4 + 4 = 0 โ
Step 6: Verify x = -2i: (-2i)ยฒ + 4 = 4iยฒ + 4 = 4(-1) + 4 = -4 + 4 = 0 โ
Answer: x = ยฑ2i