1. Solving Radical Equations
11-9
Solving Radical Equations
Warm Up
Lesson Presentation
Lesson Quiz
Holt Algebra 1

2. Warm Up
Solve each equation.
1. 3x +5 = 17
2. 4x + 1 = 2x – 3 3.
4. (x + 7)(x – 4) = 0
5. x2 – 11x + 30 = 0
6. x2 = 2x + 15 4 –2 35
–7, 4
6, 5
5, –3

3. Objective
Solve radical equations.

4. Vocabulary
radical equation
extraneous solution

5. A radical equation is an equation that contains a variable within a radical. In this course, you will only study radical equations that contain square roots.
Recall that you use inverse operations to solve equations. For nonnegative numbers, squaring and taking the square root are inverse operations. When an equation contains a variable within a square root, square both sides of the equation to solve.

7. Example 1A: Solving Simple Radical Equations
Solve the equation. Check your answer.
Square both sides.
x = 25
Check
Substitute 25 for x in the original equation. 5 5 
Simplify.

8. Example 1B: Solving Simple Radical Equations
Solve the equation. Check your answer.
Square both sides.
100 = 2x
50 = x
Divide both sides by 2.
Check
Substitute 50 for x in the original equation. 
Simplify.

9.  Check It Out! Example 1a Solve the equation. Check your answer.
Square both sides.
Simplify.
Check
Substitute 36 for x in the original equation. 
Simplify.

10.  Check It Out! Example 1b Solve the equation. Check your answer.
Square both sides.
81 = 27x
Divide both sides by 27.
3 = x
Check
Substitute 3 for x in the original equation. 
Simplify.

11.  Check It Out! Example 1c Solve the equation. Check your answer.
Square both sides.
3x = 1
Divide both sides by 3.
Check
Substitute for x in the original equation. 
Simplify.

12. Some square-root equations do not have the square root isolated
Some square-root equations do not have the square root isolated. To solve these equations, you may have to isolate the square root before squaring both sides. You can do this by using one or more inverse operations.

13. Example 2A: Solving Simple Radical Equations
Solve the equation. Check your answer.
Add 4 to both sides.
Square both sides.
x = 81
Check
9 – 4 5 
5 5

14. Example 2B: Solving Simple Radical Equations
Solve the equation. Check your answer.
Square both sides.
x = 46
Subtract 3 from both sides.
Check 
7 7

15. Example 2C: Solving Simple Radical Equations
Solve the equation. Check your answer.
Subtract 6 from both sides.
Square both sides.
5x + 1 = 16
5x = 15
Subtract 1 from both sides.
x = 3
Divide both sides by 5.

16.  Example 2C Continued Solve the equation. Check your answer. Check 

17.  Check It Out! Example 2a Solve the equation. Check your answer.
Add 2 to both sides.
Square both sides.
x = 9
Check
1 1 

18.  Check It Out! Example 2b Solve the equation. Check your answer.
Square both sides.
Subtract 7 from both sides.
x = 18
Check 
5 5

19. Check It Out! Example 2c
Solve the equation. Check your answer.
Add 1 to both sides.
Square both sides.
3x = 9
Subtract 7 from both sides.
x = 3
Divide both sides by 3.

20.  Check It Out! Example 2c Solve the equation. Check your answer.
3 3

21. Example 3A: Solving Radical Equations by Multiplying or Dividing
Solve the equation. Check your answer.
Method 1
Divide both sides by 4.
Square both sides.
x = 64

22. Example 3A Continued
Solve the equation. Check your answer.
Method 2
Square both sides.
x = 64
Divide both sides by 16.

23.  Example 3A Continued Solve the equation. Check your answer. Check
Substitute 64 for x in the original equation. 
Simplify.

24. Example 3B: Solving Radical Equations by Multiplying or Dividing
Solve the equation. Check your answer.
Method 1
Multiply both sides by 2.
Square both sides.
144 = x

25. Example 3B Continued
Solve the equation. Check your answer.
Method 2
Square both sides.
Multiply both sides by 4.
144 = x

26.  Example 3B Continued Solve the equation. Check your answer. Check
Substitute 144 for x in the original equation.
Simplify. 

27. Check It Out! Example 3a
Solve the equation. Check your answer.
Method 1
Divide both sides by 2.
Square both sides.

28. Check It Out! Example 3a Continued
Solve the equation. Check your answer.
Method 2
Square both sides.
Divide both sides by 4.
x = 121

29. Check It Out! Example 3a Continued
Solve the equation. Check your answer.
Check
Substitute 121 for x in the original equation. 
Simplify.

30. Check It Out! Example 3b
Solve the equation. Check your answer.
Method 1
Multiply both sides by 4.
Square both sides.
64 = x

31. Check It Out! Example 3b Continued
Solve the equation. Check your answer.
Method 2
Square both sides.
Multiply both sides by 16.

32. Check It Out! Example 3b Continued
Solve the equation. Check your answer.
Check
Substitute 64 for x in the original equation.
Simplify. 

33. Check It Out! Example 3c
Solve the equation. Check your answer.
Method 1
Multiply both sides by 5.
Square both sides.
Divide both sides by 4.
x = 100

34. Check It Out! Example 3c Continued
Solve the equation. Check your answer.
Method 2
Square both sides.
Multiply both sides by 25.
4x = 400
x = 100
Divide both sides by 4.

35. Check It Out! Example 3c Continued
Solve the equation. Check your answer.
Check
Substitute 100 for x in the original equation. 4
Simplify.
4 4 

36. Example 4A: Solving Radical Equations with Square Roots on Both Sides
Solve the equation. Check your answer.
Square both sides.
2x – 1 = x + 7
Add 1 to both sides and subtract x from both sides.
x = 8
Check 

37. Example 4B: Solving Radical Equations with Square Roots on Both Sides
Solve the equation. Check your answer.
Add to both sides.
Square both sides.
5x – 4 = 6
Add 4 to both sides.
5x = 10
Divide both sides by 2.
x = 2

38.  Example 4B Continued Solve the equation. Check your answer. Check
0 0

39. Check It Out! Example 4a
Solve the equation. Check your answer.
Square both sides.
Subtract x from both sides and subtract 2 from both sides.
2x = 4
x = 2
Divide both sides by 2.

40. Check It Out! Example 4a Continued
Solve the equation. Check your answer.
Check 

41. Check It Out! Example 4b
Solve the equation. Check your answer.
Add to both sides.
Square both sides.
2x – 5 = 6
2x = 11
Add 5 to both sides.
Divide both sides by 2.

42. Check It Out! Example 4b Continued
Solve the equation. Check your answer.
Check 
0 0

43. Squaring both sides of an equation may result in an extraneous solution—a number that is not a solution of the original equation.
Suppose your original equation is x = 3.
x = 3
x2 = 9
Square both sides. Now you have a new equation.
Solve this new equation for x by taking the square root of both sides.
x = 3 or x = –3

44. Now there are two solutions. One (x = 3) is the original equation
Now there are two solutions. One (x = 3) is the original equation. The other (x = –3) is extraneous–it is not a solution of the original equation. Because of extraneous solutions, it is important to check your answers.

45. Example 5A: Extraneous Solutions
Solve Check your answer.
Subtract 12 from each sides.
Square both sides
6x = 36
Divide both sides by 6.
x = 6

46.  Example 5A Continued Solve Check your answer. Check
Substitute 6 for x in the equation. 
6 does not check. There is no solution.

47. Example 5B: Extraneous Solutions
Solve Check your answer.
Square both sides
x2 = 2x + 3
x2 – 2x – 3 = 0
Write in standard form.
(x – 3)(x + 1) = 0
Factor.
x – 3 = 0 or x + 1 = 0
Zero-Product Property
x = 3 or x = –1
Solve for x.

48.   Example 5B Continued Solve Check your answer. Check
Substitute –1 for x in the equation.  –
Substitute 3 for x in the equation. 
–1 does not check; it is extraneous. The only solution is 3.

49. Check It Out! Example 5a
Solve the equation. Check your answer.
Subtract 11 from both sides.
Square both sides.
x = 5
Simplify.

50. Check It Out! Example 5a Continued
Solve the equation. Check your answer.
Check
Substitute 5 for x in the equation. 
No solution. The answer is extraneous.

51. Check It Out! Example 5b
Solve the equation. Check your answer.
Square both sides
x2 = –3x – 2
x2 + 3x + 2 = 0
Write in standard form.
(x + 1)(x + 2) = 0
Factor.
x + 1 = 0 or x + 2 = 0
Zero-Product Property
x = –1 or x = –2
Solve for x.

52. Check It Out! Example 5b Continued
Solve the equation. Check your answer.
Check
Substitute –1 for x in the equation. 
Substitute –2 for x in the equation. – 
No solutions. Both answers are extraneous.

53. Check It Out! Example 5c
Solve the equation. Check your answer.
Square both sides
x2 – 5x +4 = 0
Write in standard form.
(x – 1)(x – 4) = 0
Factor.
X – 1 = 0 or x – 4 = 0
Zero-Product Property.
x = 1 or x = 4
Solve for x.

54. Check It Out! Example 5c Continued
Solve the equation. Check your answer.
Check
Substitute 1 for x in the equation. 
Substitute 4 for x in the equation. 
1 does not check; it is extraneous. The only solution is 4.

55. Example 6: Geometry Application
A triangle has an area of 36 square feet, its base is 8 feet, and its height is feet. What is the value of x? What is the height of the triangle?
8 ft
Use the formula for area of a triangle.
Substitute 8 for b, 36 for A and for h.
Simplify.
Divide both sides by 4.

56. Example 6 Continued
A triangle has an area of 36 square feet, its base is 8 feet, and its height is feet. What is the value of x? What is the height of the triangle?
8 ft
Square both sides.
81 = x – 1
82 = x

57. Example 6 Continued
A triangle has an area of 36 square feet, its base is 8 feet, and its height is feet. What is the value of x? What is the height of the triangle?
8 ft
Check
Substitute 82 for x. 
The value of x is 82. The height of the triangle is feet.

58. Check It Out! Example 6
A rectangle has an area of 15 cm2. Its width is 5 cm, and its length is ( ) cm. What is the value of x? What is the length of the rectangle? 5
A = lw
Use the formula for area of a rectangle.
Substitute 5 for w, 15 for A, and for l.
Divide both sides by 5.

59. Check It Out! Example 6 Continued
A rectangle has an area of 15 cm2. Its width is 5 cm, and its length is ( ) cm. What is the value of x? What is the length of the rectangle? 5
Square both sides.
8 = x
The value of x is 8. The length of the rectangle is
cm.

60. Check It Out! Example 6 Continued
A rectangle has an area of 15 cm2. Its width is 5 cm, and its length is ( ) cm. What is the value of x? What is the length of the rectangle? 5
Check
A = lw
Substitute 8 for x. 

61. Lesson Quiz: Part I
Solve each equation. Check your answer. 1. 36 2. 45 3.
no solution 4. 11 5. 4 6. 4

62. Lesson Quiz: Part II
7. A triangle has an area of 48 square feet, its base is 6 feet and its height is feet. What is the value of x? What is the height of the triangle?
253; 16 ft