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# Before we do anything else, put your computers away - PowerPoint PPT Presentation

Before we do anything else, put your computers away. Imaginary Numbers. A beginning…. Before today, you couldn’t do the square root of a negative number. Today, that will change.

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put your computers away

### Imaginary Numbers

Before today, you couldn’t do the square root of a negative number.

Today, that will change.

In the beginning, mathematicians saw no need for these numbers outside of the classroom, so they game them the name “imaginary numbers”

However, electronic and other scientific applications have come to use them frequently. Unfortunately, the name, “Imaginary Numbers” has remained.

Foundation come to use them frequently. Unfortunately, the name, “Imaginary Numbers” has remained.

The basis of the imaginary numbers is the square root of -1.

It is given the letter i.

i = √-1

So √-25 = √25 x √-1 = 5i

Basically, come to use them frequently. Unfortunately, the name, “Imaginary Numbers” has remained.

Any time you see a negative under a square root, you pull its “i” out. You do this before you do anything else.

√-36 x √-9 = 6i x 3i = 18i2

Which leads to another problem… come to use them frequently. Unfortunately, the name, “Imaginary Numbers” has remained.

What in the world are we going to do with i2?

If i = √-1, then i2 = -1.

Also, i3 = -i

and i4 = 1.

Adding and Subtracting come to use them frequently. Unfortunately, the name, “Imaginary Numbers” has remained.

(3 + 4i ) + (-2 + 6i ) = (3 + -2) + ( 4i + 6i)

= 1 + 10i

Just add the “real” parts and add the “imaginary” parts separately.

(-5 + 2 come to use them frequently. Unfortunately, the name, “Imaginary Numbers” has remained.i ) – ( 2 – 6i ) = (-5 + 2i ) + ( -2 + 6i )

When you’re subtracting, change the subtraction to addition by changing all the signs following the subtraction…just like we did before with parentheses!! Then combine like terms.

= -7 + 8i

Multiplying come to use them frequently. Unfortunately, the name, “Imaginary Numbers” has remained.

3i x 4i = 12i2 (remember that i2 = -1)

= -12 Isn’t that easy?

4i ( -3 + 2i ) Just distribute!!

-12i + 8i2 (remember that i2 = -1)

= -12i -8 and we usually write the real number first so we would put -8 – 12i

More Multiplying!!! come to use them frequently. Unfortunately, the name, “Imaginary Numbers” has remained.

(-2 – 5i) (4 + 3i ) Just FOIL!!!

-8 – 6i – 20i – 15i2 (remember that i2 = -1)

-8 – 6i – 20i + 15combine like terms

= 7 – 26i isn’t that easy?

Just one more multiplying come to use them frequently. Unfortunately, the name, “Imaginary Numbers” has remained.

(3 – 5i)2 = (3 – 5i) (3 – 5i)

= 9 -15i – 15i + 25i2

= 9 -15i – 15i – 25

= -16 – 30i

Well…maybe one more come to use them frequently. Unfortunately, the name, “Imaginary Numbers” has remained.

Do you remember how multiplying conjugates got rid of the radicals?

The same thing works here. Multiplying conjugates gets rid of i.

( -3 + 2i ) ( -3 – 2i ) = 9 + 6i – 6i – 4i2

= 9 + 6i – 6i + 4

= 13

Now its up to you come to use them frequently. Unfortunately, the name, “Imaginary Numbers” has remained.

Your assignment is

5-9    pg 314    20, 22-24, 26-28, 31-33, 38- 42, 44-46, 48, 49