# Thread:

1. ## Find the largest real solution

The largest real solution for x^2/3 - 5x^1/3 + 4 = 0 would be x =

For this one I only got two solutions, 64 and 1. I thought 64 was the correct answer but apparently I got something wrong. The real answer is 8, does anyone know what I did wrong here?

2. Originally Posted by nandokommando
The largest real solution for x^2/3 - 5x^1/3 + 4 = 0 would be x =

For this one I only got two solutions, 64 and 1. I thought 64 was the correct answer but apparently I got something wrong. The real answer is 8, does anyone know what I did wrong here?
Let $u=x^{1/3}$, then we have

$u^2-5u+4=0$

$(u-4)(u-1)=0\Rightarrow{u}=1,4\Rightarrow{x}=1,64$.
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