09.12.2012 Views

Concrete mathematics : a foundation for computer science

Concrete mathematics : a foundation for computer science

Concrete mathematics : a foundation for computer science

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

56 SUMS<br />

u(x) = x and Av(x) = 2’; hence Au(x) = 1, v(x) = 2x, and Ev(x) = 2X+1.<br />

Plugging into (2.56) gives<br />

x x2” sx = x2” - t 2X+’<br />

6x = x2” - 2x+’ + c.<br />

And we can use this to evaluate the sum we did be<strong>for</strong>e, by attaching limits:<br />

f k2k = t;+‘x2” 6x<br />

k=@<br />

= x2X-2X+l ll+’<br />

= ((n-t 1)2”+’ -2n+2) - (0.2’-2’) = (n- 1)2n+’ f2.<br />

It’s easier to find the sum this way than to use the perturbation method,<br />

because we don’t have to tlrink. The ultimate goal<br />

We stumbled across a <strong>for</strong>mula <strong>for</strong> toSk

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!