Presentation on theme: "Imaginary & Complex Numbers 5-3 English Casbarro Unit 5: Polynomials."— Presentation transcript:
Imaginary & Complex Numbers 5-3 English Casbarro Unit 5: Polynomials
Definition: i is defined as. So every negative number under a square root sign can be written as (–1) times the number. Recall:. If you have, you can rewrite it as which equals 5 * i = 5 i. Now you try:
Sometimes the numbers will need to be factored before a perfect square appears. For example, is not a perfect square. But it will factor to = 5 * i * = 5 i Now you try:
i comes in groups of 4: i = ii 5 = i i 2 = - 1 i 6 = –1 i 3 = -ii 7 = -i i 4 = 1 i 8 = 1 So, to find i 542, you would have to figure out where it is in the group of 4 You just need to know the 4 542 remainder.
There are more difficult problems that you can solve that depend on your knowing the following factorizations (make sure to check out the pattern!): (x + 1) 2 = x 2 + 2x + 1 (x + 2) 2 = x 2 + 4x + 4 (x + 3) 2 = x 2 + 6x + 9 (x + 4) 2 = x 2 + 8x + 16 (x + 5) 2 = x 2 + 10x + 25 (x + 6) 2 = x 2 + 12x + 36 (x + 7) 2 = x 2 + 14x + 49 (x + 8) 2 = x 2 + 16x + 64 (x + 9) 2 = x 2 + 18x + 81 (x + 10) 2 = x 2 + 20x + 100
Completing the Square What number would I need to add to the following expressions to keep to the pattern from the previous slide? x 2 + 20x + _______x 2 + 24x + _______ x 2 + 30x + _______x 2 + 42x + _______ How would you write the factors of these expressions?
Now, let’s use what we’ve learned to solve some equations. Example 9 Find the zeroes of each function. a. f(x) = x 2 + 2x + 5 b. f(x)= x 2 + 10x + 35 Notice that each root is ±. This will always be true when you are taking a square root, so imaginary numbers will always come in pairs, one positive and one negative. Complex numbers have conjugates 5 + 2 i has the conjugate 5 – 2 i
The Quadratic Formula For any quadratic equation ax 2 + bx + c = 0, the solutions can be found using the following formula.
The quadratic formula will work for any quadratic equation, just like completing the square. In fact, the quadratic formula was discovered using the method completing the square. Proving the Quadratic Formula: ax 2 + bx + c = 0 Find the number that you have to add to make a perfect square— divide b by 2, and square it– add it to the opposite side also You must get a common denominator on the right side Factor the left side using the square
You must get a common denominator on the right side Consolidate the right side into a single fraction Take the square root of both sides Solve for x by moving to the other side. Consolidate the right side into a single fraction