题目

在ABC中，角A，B，C所对的边分别为a，b，c，且a2+b2﹣c2=ab．           （Ⅰ）求cos的值；                                            （Ⅱ）若c=2，求△ABC面积的最大值．                             答案：【考点】余弦定理；正弦定理．                                    【专题】计算题；转化思想；分析法；解三角形．                        【分析】（Ⅰ）由已知及余弦定理可得cosC的值，利用C为锐角，可求范围，从而利用二倍角的余弦函数公式可求cos的值；       ---Drinking too much cola is bad for our health.--- Yes, I _____ you.A. am mad at B. agree with C. am worried about D. am pleased with