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    Hi guys,
    I'm doing C4 right now and I was watching a hegartymaths video on parametric equations.

    I was confused because when he had the equation t^3 = -8, he made it -2.

    I have always been told in maths you can't root negative numbers??

    Thanks in advance for the help and sorry if its a really stupid question!
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    (Original post by djels013.211)
    Hi guys,
    I'm doing C4 right now and I was watching a hegartymaths video on parametric equations.

    I was confused because when he had the equation t^3 = -8, he made it -2.

    I have always been told in maths you can't root negative numbers??

    Thanks in advance for the help and sorry if its a really stupid question!
    You can't square root (or any take any nth root, where n is an even number) a negative number unless you want to step out of \mathbb{R}. Odd powers of the root, like \sqrt[3]{-1} are fine.
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    The square root of a negative number does not exist (it is not real)

    But the cube root of a negative number does exist.
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    That's cube rooting though, so it's fine. (-2)^2 is 4, so (4 * -2) is -8.
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    (Original post by djels013.211)
    Hi guys,
    I'm doing C4 right now and I was watching a hegartymaths video on parametric equations.

    I was confused because when he had the equation t^3 = -8, he made it -2.

    I have always been told in maths you can't root negative numbers??

    Thanks in advance for the help and sorry if its a really stupid question!
    you can't SQUARE root negative numbers, but you can root numbers by an odd power. This is because two negative numbers multiplied together will always make a positive number. That is why you can't square root negative numbers. However, an odd number of negative numbers multiplied together will make a negative number.

    e.g. -2x-2x-2=-8. thus cubed root of -8 is -2.

    So if x^a=-b, as long as a is an odd number, you can 'root' the value of b to find the solution. But is a is an even value, then you can't.
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    If you do a even number root of a negative number it becomes an imaginary number
 
 
 
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