Surds identity and algebraic identity statements

CMAT 2021 · Quantitative Techniques & Data Interpretation · Medium · Surds and Indices

Given below are two statements:

Statement I: 7+57−5+7−57+5=2\frac{\sqrt{7}+\sqrt{5}}{\sqrt{7}-\sqrt{5}} + \frac{\sqrt{7}-\sqrt{5}}{\sqrt{7}+\sqrt{5}} = 2

Statement II: If a+b+c=0a + b + c = 0, then (a3+b3+c3)÷abc=3(a^3 + b^3 + c^3) \div abc = 3

In light of the above statements, choose the correct answer from the options given below

  1. A.

    Both Statement I and Statement II are true

  2. B.

    Both Statement I and Statement II are false

  3. C.

    Statement I is true but Statement II is false

  4. D.

    Statement I is false but Statement II is true

Answer

D

Explanation

Statement I: (7+5)2+(7−5)27−5=2(7+5)2=12≠2\frac{(\sqrt{7}+\sqrt{5})^2 + (\sqrt{7}-\sqrt{5})^2}{7-5} = \frac{2(7 + 5)}{2} = 12 \neq 2 So Statement I is false.

Statement II: If a+b+c=0a + b + c = 0, by algebraic identity a3+b3+c3=3abca^3 + b^3 + c^3 = 3abc. Thus, (a3+b3+c3)÷abc=3(a^3 + b^3 + c^3) \div abc = 3. Statement II is true.

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