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Luisa and Jacob each solve the radical equation √5+4x = x. Luisa determines that the solution is

H= 5. Jacob thinks that the solution is a = -1. Use the space below to identify which student is
correct. Use words and mathematics to justify your answer and show any work completed to make your
selection.

User David Haddad
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1 Answer

15 votes
15 votes

Answer: Luisa is correct.

Step-by-step explanation: Luisa is correct. To find the solution to the equation, we need to isolate the radical expression on one side of the equation. If we subtract x from both sides, we get √5 + 4x - x = x - x, or √5 = 0. Since the square root of any number is always positive, this equation has no solution. Therefore, the solution is H = 5.

On the other hand, if we square both sides of the equation, we get 5 + 8x + 4x^2 = x^2. If we simplify this equation, we get x^2 + 8x - 5 = 0. This equation can be solved using the quadratic formula, which gives us x = (-8 +/- sqrt(64 + 20))/2. This simplifies to x = (-8 +/- sqrt(84))/2. The solutions to this equation are x = -1 and x = 5. However, since we squared both sides of the original equation, we have to check whether these solutions actually work in the original equation. Substituting x = -1 into the original equation gives us √5 + 4(-1) = -1, or √5 = -1. This is not a valid solution, since the square root of any number is always positive. However, substituting x = 5 into the original equation gives us √5 + 4(5) = 5, or √5 = 0. This is a valid solution, since the square root of any number is always positive. Therefore, the only solution to the original equation is x = 5, which is the solution that Luisa found.

User Nick Stemerdink
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