If a2+b2=45 and ab=18, find 1/a+1/b

If a²+b²=45 and ab=18, find 1/a+1/b

A 1/3

B 2/3

C 1/2

D Cannot be determined

Solution

Correct Answer: Option C

a2+b2 + 2ab = (a+b)2

or, 45 + 18*2 = (a+b)2

or, 81 = (a+b)2

or (a+b) = +- 9

Now, 1/a + 1/b = (a+b) /ab

= +- 9 / 18

= +- 1/2