5.9 complex numbers
TRANSCRIPT
Complex NumbersComplex Numbers
Consider the quadratic equation x2 + 1 = 0.
Solving for x , gives x2 = – 1
12 x
1x
Complex Numbers
Since there is not real number whose Since there is not real number whose square is -1, the equation has no real square is -1, the equation has no real solution. French mathematician solution. French mathematician Rene Descartes (1596 -1650) Rene Descartes (1596 -1650) proposed that proposed that i i be defined such that,be defined such that,
1i
1i
Complex Numbers
12 iNote that squaring both sides yields:therefore
and
so
and
iiiii *1* 13 2
1)1(*)1(* 224 iii
iiiii *1*45
1*1* 2246 iiii
And so on…
Finding Powers of Finding Powers of ii
The successive powers of i rotate through the four values of i, -1, -i, and 1.
in = i if n = 1, 5, 9, …
in = -1 if n = 2, 6, 10, …
in = -i if n = 3, 7, 11, …
in = 1 if n = 4, 8, 12, …
then,1- If i
12 i
ii 3
14 i
ii 5
16 i
ii 7
18 i
*For larger exponents, divide the exponent by 4, then use the remainder
as your exponent instead.
Example: ?23 i3 ofremainder a with 5
4
23
.etcii - which use So, 3
ii 23
Real NumbersImaginary Numbers
Real numbers and imaginary numbers are subsets of the set of complex numbers.
Complex Numbers
Imaginary UnitImaginary Unit• Until now, you have always been told
that you can’t take the square root of a negative number. If you use imaginary units, you can!
• The imaginary unit is ¡.• ¡= • It is used to write the square root of
a negative number.
1
Property of the square root Property of the square root of negative numbersof negative numbers
• If r is a positive real number, then
r ri
Examples:
3 3i 4 4i i2
ExamplesExamples2)3( 1. i
22 )3(i)3*3(1
)3(13
26103 Solve 2. 2 x
363 2 x122 x
122 x
12ix 32ix
Complex NumbersComplex Numbers• A complex number has a real part &
an imaginary part.• Standard form is:
bia
Real part Imaginary part
Example: 5+4iExample: 5+4i
Adding and SubtractingAdding and Subtracting
To Add or Subtract Complex Numbers
1. Change all imaginary numbers to bi form.
2. Add (or subtract) the real parts of the complex numbers.
3. Add (or subtract) the imaginary parts of the complex numbers.
4. Write the answer in the form a + bi.
Adding and SubtractingAdding and Subtracting(add or subtract the real parts, then (add or subtract the real parts, then add or subtract the imaginary parts)add or subtract the imaginary parts)
Ex: )33()21( ii )32()31( ii
i52
Ex: )73()32( ii )73()32( ii
i41
Ex: )32()3(2 iii )32()23( iii
i21
MultiplyingMultiplying
To Multiply Complex Numbers
1. Change all imaginary numbers to bi form.
2. Multiply the complex numbers as you would multiply polynomials.
3. Substitute –1 for each i2.
4. Combine the real parts and the imaginary parts. Write the answer in a + bi form.
MultiplyingMultiplyingTreat the i’s like variables, then Treat the i’s like variables, then change any that are not to the change any that are not to the
first powerfirst power
Ex: )3( ii 23 ii
)1(3 i
i31
Ex: )26)(32( ii 2618412 iii
)1(62212 i62212 i
i226
CAUTION!CAUTION!
?24
2424 ii
22 2i 22
824
DividingDividing
To Divide Complex Numbers
1. Change all imaginary numbers to bi form.
2. Rationalize the denominator by multiplying both the numerator and the denominator by the conjugate of the denominator.
3. Substitute –1 for each i2.
DividingDividing
Examples:
i
i
34
34
i
i
i
i
34
34
34
34
2316
3434
i
ii
916
92416 2ii25
247 i
53
5
53
5
i
53
53
53
5
i
i
i
259
)53(5
i
i
59
)5515 i
14
)5515 i
i
i
i
iEx
21
21*
21
113 :
)21)(21(
)21)(113(
ii
ii
2
2
4221
221163
iii
iii
)1(41
)1(2253
i
41
2253
i
5
525 i
5
5
5
25 i
i 5