8/2/2019 Pre Algebra Lesson 3 4

1/21

3-4 Using Formulas

Objective: Solve problems using formulas.

8/2/2019 Pre Algebra Lesson 3 4

2/21

5-Minute Check

Solve each equation. Check your solution.

1. x/3 = -6

8/2/2019 Pre Algebra Lesson 3 4

3/21

5-Minute Check

Solve each equation. Check your solution.

1. x/3 = -6 -18

8/2/2019 Pre Algebra Lesson 3 4

4/21

5-Minute Check

Solve each equation. Check your solution.

1. x/3 = -6

2. -3x = -6

8/2/2019 Pre Algebra Lesson 3 4

5/21

5-Minute Check

Solve each equation. Check your solution.

1. x/3 = -6

2. -3x = -6 2

8/2/2019 Pre Algebra Lesson 3 4

6/21

5-Minute Check

Solve each equation. Check your solution.

1. x/3 = -6

2. -3x = -6

3. x/-2 = -16

8/2/2019 Pre Algebra Lesson 3 4

7/21

5-Minute Check

Solve each equation. Check your solution.

1. x/3 = -6

2. -3x = -6

3. x/-2 = -16 32

8/2/2019 Pre Algebra Lesson 3 4

8/21

5-Minute Check

Solve each equation. Check your solution.

1. x/3 = -6

2. -3x = -6

3. x/-2 = -16

4. -2x = 16

8/2/2019 Pre Algebra Lesson 3 4

9/21

5-Minute Check

Solve each equation. Check your solution.

1. x/3 = -6

2. -3x = -6

3. x/-2 = -16

4. -2x = 16 -8

8/2/2019 Pre Algebra Lesson 3 4

10/21

5-Minute Check

Solve each equation. Check your solution.

1. x/3 = -6

2. -3x = -6

3. x/-2 = -16

4. -2x = 16

5. 12x = -156

8/2/2019 Pre Algebra Lesson 3 4

11/21

5-Minute Check

Solve each equation. Check your solution.

1. x/3 = -6

2. -3x = -6

3. x/-2 = -16

4. -2x = 16

5. 12x = -156 -13

8/2/2019 Pre Algebra Lesson 3 4

12/21

3-4 Using Formulas

A formula shows the relationship between certainquantities.

Variables are used to represent these qualities.

8/2/2019 Pre Algebra Lesson 3 4

13/21

3-4 Using Formulas

Write a formula for the diameter of a circle, given it radius r.

It is often helpful to draw a picture.

Let d = diameter.

Let r = radius

The radius is equal to half the diameter of a circle.

r = d

So, d = 2r.

8/2/2019 Pre Algebra Lesson 3 4

14/21

3-4 Using Formulas

Example

Use the formula d = 2r to find the radius of a circle that has a

diameter of 18 meters.

8/2/2019 Pre Algebra Lesson 3 4

15/21

3-4 Using Formulas

Example

Use the formula d = 2r to find the radius of a circle that has a

diameter of 18 meters.

d = 2r Diameter formula.

8/2/2019 Pre Algebra Lesson 3 4

16/21

3-4 Using Formulas

Example

Use the formula d = 2r to find the radius of a circle that has a

diameter of 18 meters.

d = 2r Diameter formula.18 = 2r Substitute 18 for d.

8/2/2019 Pre Algebra Lesson 3 4

17/21

3-4 Using Formulas

Example

Use the formula d = 2r to find the radius of a circle that has a

diameter of 18 meters.

d = 2r Diameter formula.18 = 2r Substitute 18 for d.

18/2 = 2r/2 Divide each side by 2.

8/2/2019 Pre Algebra Lesson 3 4

18/21

3-4 Using Formulas

Example

Use the formula d = 2r to find the radius of a circle that has a

diameter of 18 meters.

d = 2r Diameter formula.18 = 2r Substitute 18 for d.

18/2 = 2r/2 Divide each side by 2.

9 = r

8/2/2019 Pre Algebra Lesson 3 4

19/21

3-4 Using Formulas

Example

Use the formula d = 2r to find the radius of a circle that has a

diameter of 18 meters.

d = 2r Diameter formula.18 = 2r Substitute 18 for d.

18/2 = 2r/2 Divide each side by 2.

9 = r

A circle with a diameter of 18 meters has a radius of 9meters.

8/2/2019 Pre Algebra Lesson 3 4

20/21

3-4 Using Formulas

Integration

An equilateral triangle is a triangle whose three sides are all

equal in length. Give a formula for the perimeter of any

equilateral triangle.

8/2/2019 Pre Algebra Lesson 3 4

21/21

3-4 Using Formulas

Integration

An equilateral triangle is a triangle whose three sides are all

equal in length. Give a formula for the perimeter of any

equilateral triangle.

Answer: p = 3s where p = perimeter and s = length of each

side.