Correct option is B
Given:
a = (√5 − 2)/(√5 + 2)
Formula:
(a + 1/a)² = a² + 1/a² + 2
Solution:
a = (√5 − 2)/(√5 + 2)
Rationalising,
a = (√5 − 2)²/(5 − 4)
= 9 − 4√5
Therefore,
1/a = 9 + 4√5
Now,
A.
a + 1/a
= 9 − 4√5 + 9 + 4√5
= 18
Therefore, A → III.
B.
1/a − a
= 9 + 4√5 − 9 + 4√5
= 8√5
Therefore, B → I.
Also,
C.
a² + 1/a²
= (a + 1/a)² − 2
= 18² − 2
= 324 − 2
= 322
Therefore,
1/2(a² + 1/a²)
= 322/2
= 161
Therefore, C → II.
Now, D.
1/a² − a²
= (1/a − a)(1/a + a)
= 8√5 × 18
= 144√5
Therefore, D → IV.
Hence, the correct matching is:
A-III, B-I, C-II, D-IV
Hence, the correct answer is Option (b).