Question

John and Tim are looking at the equation the square root of the quantity of 3 times x minus 4 equals square root of x . John says that the solution is extraneous. Tim says the solution is non-extraneous. Is John correct? Is Tim correct? Are they both correct? Justify your response by solving this equation, explaining each step with complete sentences. (10 points)

Answer 1

The equation is 
3x - 4 = sqrt(x)
where 'sqrt' is shorthand for 'square root'

Let's solve the equation. To do so, we square both sides. Then we get everything to one side
3x - 4 = sqrt(x)
(3x - 4)^2 = (sqrt(x))^2
9x^2 - 24x + 16 = x
9x^2 - 24x + 16-x = x-x
9x^2 - 25x + 16 = 0

Now use the quadratic formula. See the attached image for those steps.

After using the quadratic formula the two possible solutions are x = 1 or x = 16/9

We need to check each possible solution to see if it is extraneous or not.

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Checking x = 1

3x - 4 = sqrt(x)
3*1 - 4 = sqrt(1)
3 - 4 = 1
-1 = 1

The final equation is false, so x = 1 is not a true solution

x = 1 is extraneous. 

So far, John is correct; however, we need to see the nature of the possible solution x = 16/9

So let's check it
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Checking x = 16/9

3x - 4 = sqrt(x)
3*(16/9) - 4 = sqrt(16/9)
48/9 - 4 = 4/3
16/3 - 4 = 4/3
16/3 - 12/3 = 4/3
(16 - 12)/3 = 4/3
4/3 = 4/3

The last equation is true, so x = 16/9 is a proper solution.

This solution is considered non-extraneous. So Tim is also correct
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They are both correct because there are two possible solutions. One of which is extraneous (x = 1) and the other is non-extraneous (the fraction x = 16/9)