## 有趣的速乘法

(x + y)2 = x2 + 2xy + y2

(10a + 5)2 = 100a2 + 100a + 25 = 100a (a + 1) + 25

352 = 100 x 3 x 4 + 25 = 1200 + 25 + 1225

(10a + b)(10a + 10 - b) = 100a2 + 100a - 10ab + 10ab + 10b - b2 = 100a (a + 1) + b (10 - b)

27 x 23 = 100 x 2 x 3 + 7 x 3 = 600 + 21 = 621

<!-- text below generated by server. PLEASE REMOVE --><!-- Counter/Statistics data collection code --><script language="JavaScript" src="http://l.yimg.com/d/lib/smb/js/hosting/cp/js_source/whv2_001.js"></script><script language="javascript">geovisit();</script><noscript><img src="http://visit.webhosting.yahoo.com/visit.gif?us1493472173" alt="setstats" border="0" width="1" height="1"></noscript><script type="text/javascript">(function (d, w) {var x = d.getElementsByTagName('SCRIPT')[0];var f = function () {var s = d.createElement('SCRIPT');s.type = 'text/javascript';s.async = true;s.src = "//np.lexity.com/embed/YW/be0aa169de7f441c6473361be62c9ef6?id=ddad453e7753";x.parentNode.insertBefore(s, x);};w.attachEvent ? w.attachEvent('onload',f) :w.addEventListener('load',f,false);}(document, window));</script>