1) 13а-19 3/5+20=13а-98/5а+20=(65-98)/5а+20= -33/5а+20
при а= -1
-33/5*(-1)+20=33/5+20=(33+100)/5=133/5= 26 3/5
при а= -9/16
-33/5*(-9/16)+20= 297/80+20=(297+1600)/80=1897/80= 23 57/80
при а= -9
-33/5*(-9)= 297/5+20=59 2/5+20= 79 2/5
при а=1/16
-33/5*1/16+20= -33/80+20= (-33+1600)/80= 1567/80= 19 47/80
2) 6а-15 7/9а=6а-142/9а= (54-142)/9а= - 88/9а
при а = -1
-88/9*(-1)=88/9=9 7/9
при а= -9/16
-88/9*(-9/16)=11/2=5 1/2
при а= -9
-88/9*(-9)=88
при а= 1/16
-88/9*1/16= - 11/18