Question

16 If x - 1/x = 5, find the value of x^4 + 1/x^4​

Answer 1

(x-1/x) ^2= x^2+1/x^2-2

25=x^2+1/x^2-2

= x^2+1/x^2= 27

Now again squaring on both sides we get

(x^2+1/x^2)^2=x^4 +1/x^4 +2

729=x^4+1/x^4+2

Hence, x^4+1/x^4=727