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Equations containing radicals
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Squaring both sides can introduce extraneous solutions.
Always substitute back into the original equation!
If there are two radicals:
For : must have
Solve: โx = 5
Step 1: Square both sides: (โx)ยฒ = 5ยฒ x = 25
Step 2: Check the solution: โ25 = 5 โ
Answer: x = 25
Solve:
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For : can be any real number
Solve:
Square both sides:
Check: โ
Square both sides:
Solve for :
Check: โ
Answer:
Solve: โ(x + 3) = 4
Step 1: Square both sides: (โ(x + 3))ยฒ = 4ยฒ x + 3 = 16
Step 2: Solve for x: x = 16 - 3 x = 13
Step 3: Check the solution: โ(13 + 3) = โ16 = 4 โ
Answer: x = 13
Solve:
Step 1: Isolate the radical
Step 2: Square both sides
Solve: โ(2x - 1) = x - 2
Step 1: Square both sides: (โ(2x - 1))ยฒ = (x - 2)ยฒ 2x - 1 = xยฒ - 4x + 4
Step 2: Rearrange to standard form: 0 = xยฒ - 4x - 2x + 4 + 1 0 = xยฒ - 6x + 5
Step 3: Factor: 0 = (x - 5)(x - 1)
Step 4: Solve: x = 5 or x = 1
Step 5: Check x = 5: โ(2(5) - 1) = โ9 = 3 5 - 2 = 3 โ
Step 6: Check x = 1: โ(2(1) - 1) = โ1 = 1 1 - 2 = -1 โ x = 1 is EXTRANEOUS
Answer: x = 5
Solve: โ(x + 7) - โ(x - 5) = 2
Step 1: Isolate one radical: โ(x + 7) = 2 + โ(x - 5)
Step 2: Square both sides: x + 7 = (2 + โ(x - 5))ยฒ x + 7 = 4 + 4โ(x - 5) + (x - 5) x + 7 = x - 1 + 4โ(x - 5)
Step 3: Simplify: x + 7 - x + 1 = 4โ(x - 5) 8 = 4โ(x - 5) 2 = โ(x - 5)
Step 4: Square again: 4 = x - 5 x = 9
Step 5: Check x = 9: โ(9 + 7) - โ(9 - 5) = โ16 - โ4 = 4 - 2 = 2 โ
Answer: x = 9
Solve:
Step 1: Square both sides
Solve: โ(x + 1) = 2
Step 1: Cube both sides: (โ(x + 1))ยณ = 2ยณ x + 1 = 8
Step 2: Solve for x: x = 7
Step 3: Check: โ(7 + 1) = โ8 = 2 โ
Step 4: Note about odd roots: Unlike even roots, odd roots can have negative radicands For example, โ(-8) = -2
Answer: x = 7
Step 3: Solve
Check: โ
Answer:
Step 2: Rearrange to standard form
Step 3: Factor
Step 4: Solve
Step 5: Check both solutions
For : and โ
For : and โ
Answer: only (x = 2 is extraneous)