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# 9.1 Square Roots and the Pythagorean Theorem - PowerPoint PPT Presentation

9.1 Square Roots and the Pythagorean Theorem. By definition Ö 25 is the number you would multiply times itself to get 25 for an answer. Because we are familiar with multiplication, we know that Ö 25 = 5.

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Presentation Transcript

By definition Ö25 is the number you would multiply times itself to get 25 for an answer.

Because we are familiar with multiplication, we know that Ö25 = 5

Numbers like 25, which have whole numbers for their square roots, are called perfect squares

You need to memorize at least the first 15 perfect squares

Square root

Perfect square

Perfect square

1

81

Ö1 = 1

Ö81 = 9

4

100

Ö4 = 2

Ö100 = 10

9

121

Ö9 = 3

Ö121 = 11

16

144

Ö16 = 4

Ö144 = 12

25

169

Ö25 = 5

Ö169 = 13

36

196

Ö36 = 6

Ö196 = 14

49

225

Ö49 = 7

Ö225 = 15

64

Ö64 = 8

Every whole number has a square root

Most numbers are not perfect squares, and so their square roots are not whole numbers.

Most numbers that are not perfect squares have square roots that are irrational numbers

Irrational numbers can be represented by decimals that do not terminate and do not repeat

The decimal approximations of whole numbers can be determined using a calculator

Find the square roots of the given numbers

If the number is not a perfect square, use a calculator to find the answer correct to the nearest hundredth.

81

37

158

Find the square roots of the given numbers

If the number is not a perfect square, use a calculator to find the answer correct to the nearest thousandth.

a

b

9.1 Square Roots and the Pythagorean Theorem

The Pythagorean Theorem

For any right triangle, the sum of the squares of the lengths of the legs a and b, equals the square of the length of the hypotenuse.

a2 + b2 = c2

6

8

9.1 Square Roots and the Pythagorean Theorem

Find c.

a2 + b2 = c2

4

6

9.1 Square Roots and the Pythagorean Theorem

Find c.

a2 + b2 = c2

a

8

9.1 Square Roots and the Pythagorean Theorem

Find a.

a2 + b2 = c2

60 ft

9.1 Square Roots and the Pythagorean Theorem

The length of each side of a softball field is 60 feet. How far is it from home to second?

602 + 602 = c2

3600 + 3600 = 7200

c2 = 7200

Solving x2 = d by Finding Square Roots

• If d is positive, then x2 = d has two solutions

• The equation x2 = 0 has one solutions:

• If d is negative, then x2 = d has no solution.

Solve

• x2 = 49

• x2 = 12

• x2 = 0

• x2 = -9

Solve

• 3x2 +1 = 76

• 4x2 + 6 = 70

• 5x2 – 7 = 18

• 3x2 – 10 = 38

y = ax2 + bx + c

Vertex

x

Vertex

The graph of a quadratic function is a parabola.

A parabola can open up or down.

If the parabola opens up, the lowest point is called the vertex.

If the parabola opens down, the vertex is the highest point.

NOTE: if the parabola opened left or right it would not be a function!

a > 0

x

a < 0

The parabola will open up when the a value is positive.

The standard form of a quadratic function is

y = ax2 + bx + c

The parabola will open down when the a value is negative.

y

x

Parabolas have a symmetric property to them.

If we drew a line down the middle of the parabola, we could fold the parabola in half.

We call this line the line of symmetry.

Or, if we graphed one side of the parabola, we could “fold” (or REFLECT) it over, the line of symmetry to graph the other side.

The line of symmetry ALWAYS passes through the vertex.

When a quadratic function is in standard form

For example…

Find the line of symmetry of y = 3x2 – 18x + 7

y = ax2 + bx + c,

The equation of the line of symmetry is

Using the formula…

This is best read as …

the opposite of b divided by the quantity of 2 times a.

Thus, the line of symmetry is x = 3.

y = –2x2 + 8x –3

We know the line of symmetry always goes through the vertex.

STEP 1: Find the line of symmetry

Thus, the line of symmetry gives us the x – coordinate of the vertex.

STEP 2: Plug the x – value into the original equation to find the y value.

y = –2(4)+ 8(2) –3

y = –2(2)2 + 8(2) –3

To find the y – coordinate of the vertex, we need to plug the x – value into the original equation.

y = –8+ 16 –3

y = 5

Therefore, the vertex is (2 , 5)

The standard form of a quadratic function is given by y = ax2 + bx + c

STEP 1: Find the line of symmetry

STEP 2: Find the vertex

STEP 3: Find two other points and reflect them across the line of symmetry. Then connect the five points with a smooth curve.

x

Let's Graph ONE! Try …

y = 2x2 – 4x – 1

STEP 1: Find the line of symmetry

Thus the line of symmetry is x = 1

x

Let's Graph ONE! Try …

y = 2x2 – 4x – 1

STEP 2: Find the vertex

Since the x – value of the vertex is given by the line of symmetry, we need to plug in x = 1 to find the y – value of the vertex.

Thus the vertex is (1 ,–3).

x

Let's Graph ONE! Try …

y = 2x2 – 4x – 1

STEP 3: Find two other points and reflect them across the line of symmetry. Then connect the five points with a smooth curve.

For y = -x2 - 2x + 8 identify each term, graph the equation, find the vertex, and find the solutions of the equation.

-Vertex:

x =(-b/2a)

x= -(-2/2(-1))

x= 2/(-2)

x= -1

Solve for y:

y = -x2 -2x + 8

y = -(-1)2 -(2)(-1) + 8

y = -(1) + 2 + 8

y = 9

Vertex is (-1, 9)

The quadratic formula allows you to find the roots of a quadratic equation (if they exist) even if the quadratic equation does not factorise.

The formula states that for a quadratic equation of the form :

ax2 + bx + c = 0

The roots of the quadratic equation are given by :

Use the quadratic formula to solve the equation :

x2 + 5x + 6 = 0

Solution:

x2 + 5x + 6= 0

a = 1 b = 5 c = 6

x = - 2 or x = - 3

These are the roots of the equation.

Use the quadratic formula to solve the equation :

8x2 - 22x + 15= 0

Solution:

8x2 - 22x + 15= 0

a = 8 b = -22 c = 15

x = 3/2 or x = 5/4

These are the roots of the equation.

Use the quadratic formula to solve for x to 2 decimal places.

2x2 + 3x - 7= 0

Solution:

2x2 + 3x – 7 = 0

a = 2 b = 3 c = - 7

x = 1.27 or x = - 2.77

These are the roots of the equation.

-

±

-

2

b

b

4

ac

=

x

2

a

9.5 Problem Solving Using the Discriminant

The number of solutions in a quadratic equation

Consider the equation ax2 + bx + c = 0

• If b2 – 4ac > 0, then the equation has 2 solutions.

• If b2 – 4ac = 0, then the equation has 1 solution.

• If b2 – 4ac < 0, then the equation has no solution.

Find the discriminant of 3x2 + x – 2 = 0 and tell the nature of its roots.

Discriminant = b2 – 4ac = 12 – 4(3)(-2) = 1 – (-24) = 1 + 24 = 25

So, there are two solutions

Determine the number of solutions

• 2x2 – x + 3 = 0

• x2 + x + 4 = 0

• 3x2 –5x - 3 = 0

• 2x2 – x - 9 = 0

Match the discriminant with the graph

• b2 – 4ac = 7 b. b2 – 4ac = -2 c. b2 – 4ac = 0

• Draw the graph of the equation obtained by replacing the inequality sign by an equal sign. Use a dashed line if the inequality is < or >. Use a solid line if the inequality is ≤ or ≥.

• Check a point in each of the two regions of the plane determined by the graph of the equation. If the point satisfies the inequality, then shade the region containing the point.

Steps for Drawing the Graph of an Inequality in Two Variables

Solve y > x2