First, simplify the equation:
3x+2x−4=2(x+9)−(7−1x)
3x+2x−4=2x+18−7+1x
x−15=−1x
x2−15x=−1
x2+1=15x
Now plug it into x2+1x:
=(15x)x
=15
3x + 2/x - 4 = 2(x + 9) - (7 - 1/x) ==> 3x + 2/x - 4 = 2x + 18 - 7 + 1/x ==> x + 1/x = 15 ==> x^2 + 1 = 15x. Therefore, (x^2 + 1) / x = 15x / x = 15