学习几何不能做一题只会一题，要学会变式原题，以不变的规律应付万变的题B所谓变式题，就是要找出在条件不变的前提下，该题有无与本身相应的结论；或把题中的条件加强（或减弱）能否得出相应结论．原题在已知锐角thABC的外面作正方形ABDL’与ACF’C求证：（1）BC二CF；（）BC Learning geometry can not do only one problem, to learn the original variant, to deal with the ever-changing problem of changing the B variable problem, is to find out whether the problem under the premise of the same conditions Corresponding conclusions with itself; or whether the conditions in the question can be strengthened (or weakened) to draw conclusions. The original question is squared out of the known acute angle thABC as square ABDL’ and ACF’C. Proof: (1) BC two CF; () BC