а) 36/(13-11)(13+11)=36/2*24=36/48=3/4
б) 79²-65²/420=(79-65)*(79+65)/420=14*144/420=2016/420=24/5
в) 53²-27²/79²-51²=(53-27)*(53+27)/(79-51)*(79+51)=26*80/28*130=2080/3640=4/7
г)53²-32²/61²-44²=(53-32)*(53+32)/(61-44)*(61+44)=21*85/17*105=1785/1785=1