Simplification - Quantitative Aptitude (MCQ) questions for Q. 21223

Q.  3 of the 4 expressions (1), (2), (3) & (4) given below are exactly equal . Which of the expression is not equal to the other four expressions?
- Published on 25 Apr 16

a. (A + B)2 - 4AB
b. (A – B)2 + 4AB
c. A2 + B2 - 4AB + 2AB
d. A2 – B2 + 2B(B – A)

ANSWER: (A – B)2 + 4AB
 
1) (A + B)2 – 4AB = A2 + 2AB + B2 - 4AB = A2 + B2 - 2AB
2) (A – B)2 + 4AB = A2 – 2AB + B2 + 4AB = A2+ B2 + 2AB
3) A2 +B2 – 4AB + 2AB = A2 + B2 - 2AB
4) A2 – B2 + 2B(B – A) = A2 – B2 + 2B2 – 2AB = A2 + B2 – 2AB

Therefore, (1) = (3) = (4) ≠ (2)
Therefore, expression (2) is wrong

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