(9 + √80)1.5 is equal to

A 28 + 37√5

B 38 + 35√5

C 38 + 37√5

D 38 + 17√5

E None of these

Solution

Correct Answer: Option D

(9 + √80)1.5

= (9 + 4√5)1.5

= (4+5+ 2 × 2 × √5)3/2

= (22+(√5)2+2×2×√5)3/2

[Using the formula: (a + b)2 = a2 + b2 + 2ab and (a+b)3=(a3+b3+3a2b+3ab2)]

= [(2+√5)2]3/2

= (2+√5)3

= 8 + 5√5 + 12√5 + 30

= 38+ 17√5

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