2000 General Studies, all questions
UPSC Prelims 2000 · General Studies
Question 132: Basic Numeracy
If X = –2, then X³ – X² – X – 1 is equal to
a1
b–3
c–11
d–15
AnswerThe answer is (c).
Put X = -2. Then X cubed is -8, X squared is 4, and -X is +2. So X^3 - X^2 - X - 1 = -8 - 4 + 2 - 1 = -11. The usual slips are with signs: -X is +2, not -2, and X squared is +4.
Why each option is right or wrong
- (a) 1 comes from sign errors in the cube or the square.
- (b) -3 comes from taking -X squared as +4.
- (c) Right: -8 - 4 + 2 - 1 = -11.
- (d) -15 comes from taking -X as -2 instead of +2.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2000, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.