s+2t=7,5s-3t=9

s+2t=7,5s-3t=9
s+2t=7,5s-3t=9

s+2t=7,5s-3t=9
s+2t=7﹙1﹚
5s-3t=9﹙2﹚
﹙1﹚×5得
5s＋10t=35﹙3﹚
﹙3﹚－﹙1﹚得13t=26
t=2
把t=2代入s+2t=7得s＋2×2=7
s=3
∴t=2,s=3

s+2t=7 得到5s+10t=35
又由于5s-3t=9，所以13t=26, 得到t=2
于是s=3