a, cho tam giac ABC va tam giac A\(_1\)B\(_1\)C\(_1\) co AB=A\(_1\)B\(_1\). AC=A\(_1\)C\(_1\) va BC> B\(_1\)C\(_1\). So sanh so do cua 2 goc A va A\(_1\)
b,cho tam giac ABC va tam giac A\(_1\)B\(_1\)C\(_1\) co AB=A\(_1\)B\(_1\). AC=A\(_1\)C\(_1\) va A>A\(_1\).chung minh rang BC>B\(_1\)C\(_1\)