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# Triangle Inequality questions Watch

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1. right the question is prove that |b|<1/2 implies |(b^3) -1|> 7/8

and the solution goes |b^3 - 1| >= ||b^3| - 1|>= 1-|b^3|... and i don't get they got to the last part

Its probably sdomething very simple if someone could explain that'd be great

Thanks
2. (Original post by _-_MandsSs_-_)
right the question is prove that |b|<1/2 implies |(b^3) -1|> 7/8

and the solution goes |b^3 - 1| >= ||b^3| - 1|>= 1-|b^3|... and i don't get they got to the last part

Its probably sdomething very simple if someone could explain that'd be great

Thanks
Well given the restriction on b, is positive or negative? Hence when you remove the outer modulus signs .... That final ">=" could be replaced with just "=".
3. Start with what you're given being equivalent to -1/2 < b < 1/2

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Updated: December 22, 2010
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