Question

if x=9 -4√5 find the value of x+1/x​

Answer 1

Answer:

x= 9 - 4 √5.

Since (a+b)(a - b) = a^2 - b^2

(9 - 4 √5)(9 + 4 √5) = 81 - 80 = 1

=>9 - 4 √5 = 1/(9 +4 √5) which is ‘x’

Therefore we can write 1/x = 9 + 4 √5

=> x + 1/x = (9 - 4 √5) + (9 + 4 √5) = 9 + 9 =18

.

.

.

.

.

.

Another method

Firstly rationalise the term 1/x from there we get value 9+4root5

then put value into x+1/x

then we get answer 18......