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Bunuel
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This looks like a job for a substitution (like we had to do OFTEN in calculus.)
Let x^(1/3)=u
Substitute: u^2+u-2≤0 Factor: (u+2)(u-1)≤0
So if this were an equality (instead of an inequality): u=-2 or u=1

Now let’s figure out the inequality. Let’s check a number on each side of our answers so we know which side of the answer makes the equation true. We’ll substitute the u back to x afterward.

Try: (u+2)(u-1) Evaluate (is ≤0?):

-3 (neg)(neg) NOT true
-1 (pos)(neg) TRUE
0 (pos)(neg) TRUE
2 (pos)(pos) NOT true

So, -2≤u≤1
Unsubstitute: u=x^(1/3)

So -2≤x^(1/3)≤1 Cube it all: -8≤x≤1

A! Tah Dah!
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