If x - 1/x = 4, what is the value of x^2 + 1/x^2?
Answer and explanation
Correct answer: A. 18
- Step 1: Square both sides: (x - 1/x)^2 = x^2 - 2 + 1/x^2 = 4^2 = 16. Step 2. x^2 + 1/x^2 = 16 + 2 = 18. Answer: 18. Why not the others: 16 evaluates 4^2 alone; 14 erroneously subtracts 2 instead of adding 2; 20 erroneously adds 4 instead of 2.
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