a+ax2+ax3+...+ax49+ax50=12750
ax(1+2+3+...+49+50)=12750
ax1275=12750
a=12750:1275
a=10
Ta có : a + a × 2 + a × 3 + a × 4 + … + a × 49 + a × 50 = 12750
<=> a.(1 + 2 + 3 + ...... + 50) = 12750
=> a.1275 = 12750
=> a = 12750 : 1275
=> a = 10
a x ( 2 + 3 + 4 + ....+ 49 + 50) = 12750
a x 1275 = 12750
a = 12750 : 1275
a = 10
Vậy a = 10