MCQ practice · SSC General Mathematics Board questions · Chapter 3: Algebraic Expressions
Which one of the following is the value of x³ + 1/x³?
Think it through first, then pick an option.
- a 0
- b 2√5
- c 3√5
- d 8√5
Answer and explanation
Correct answer: b 2√5
x + 1/x = √5: x³ + 1/x³ = (√5)³ − 3√5 = 5√5 − 3√5 = 2√5.
Why the other options are wrong
- a 0: 0 is the value when x + 1/x = √3; here x + 1/x = √5.
- c 3√5: 3√5 is the part to subtract (3k); it is not the answer.
- d 8√5: 8√5 = 5√5 + 3√5: the term has been added instead of subtracted.
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