Posted by **krista** on Tuesday, April 13, 2010 at 9:35pm.

show that k(x)= (5x^3) + (5/x^3) - x- (1/x)

- math-191 -
**krista**, Tuesday, April 13, 2010 at 9:36pm
^ sorry didn't finish: show that k(x)= k(1/x)

- math-191 -
**Reiny**, Tuesday, April 13, 2010 at 9:39pm
let me rewrite k(x)

k(x) = 5(x^3) + 5(1/x^3) - x/1 - 1/x

it should be intuitively obvious that

k(x) = k(1/x)

- math-191 -
**krista**, Tuesday, April 13, 2010 at 9:41pm
yea i realize that but the question says "show" that they equal each other. im thinking possibly by some sort of identity or something.

- math-191 -
**Reiny**, Tuesday, April 13, 2010 at 9:45pm
sub 1/x for x

k(1/x) = 5(1/x^3) + 5/(1/x^3) - 1/x - 1/(1/x)

= 5/x^3 + 5x^3 - 1/x - x

= the original k(x) , just the order of writing down the terms has changed.

- math-191 -
**krista**, Tuesday, April 13, 2010 at 9:50pm
ohh i see duh!! lol thanks =)

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