Question 893932

Hi, I was working on the problem x^2+2x-15=0 and when I simplified, I got to x^3=7.5. I was wondering how, since this is a quadratic equation, you recieve that into two answers instead of one. Thank you!
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For starters, {{{x^2 + 2x <> 3x^3}}}. I have no idea how you got 7.5!!