COMPLETING THE SQUARE METHOD EXAMPLES WITH ANSWERS

Example 1 :

Solve by completing the square method 

x2 – (√3 + 1)x + √3 = 0 

Solution :

x2 – (√3 + 1)x + √3 = 0 

x2 – (√3 + 1)x  =  -√3

x2 – (√3 + 1)x + [(√3 + 1)/2]2  =  -√3 + [(√3 + 1)/2]2

[x - (√3 + 1)/2]2  =  -√3 + [(√3 + 1)2 / 4]

[x - (√3 + 1)/2]2  =  (-4√3 + √32 + 2√3 + 1)/4

[x - (√3 + 1)/2]2  =  (√32 - 2√3 + 1)/4

[x - (√3 + 1)/2]2  =  [ (√3 - 1)/2 ]2

[x - (√3 + 1)/2]2  =  [ (√3 - 1)/2 ]2

[x - (√3 + 1)/2]  =  ± (√3 - 1)/2

x - (√3+1)/2  =  (√3-1)/2

x  =  (√3-1)/2 + (√3+1)/2

x  =  2√3/2

x  =  √3

x - (√3+1)/2  =  -(√3-1)/2

 =  -(√3-1)/2 + (√3+1)/2

x  =  2/2

x  =  1

Example 2 :

Solve by completing the square method 

(5x + 7)/(x – 1)  =  3x + 2

Solution :

(5x + 7)  =  (3x + 2)(x – 1)

5x + 7  =  3x² – 3x + 2x – 2

3x² – 3x + 2x – 2 – 5x – 7  =  0

3x² – 6x – 9  =  0

Divide the entire equation by 3, we get

x² – 2x – 3  =  0

x² – 3x + x – 3  =  0

x (x – 3) + 1 (x – 3)  =  0

(x – 3)(x + 1)  =  0

x - 3  =  0

x  =  3

x + 1  =  0

x  =  -1

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