a + a x 2 + a x 3 + a x 4 + ... + a x 49 + a x 50 = 12750
a x ( 1 + 2 + 3 + 4 + ..+ 49 + 50 ) = 12750
a x 1275 = 12750
a = 12750 : 1275
a = 10
Vậy a = 10
Giải:
Ta có:a*1+a*2..................a*50=12750
Vậy a*(1+2+3+..................+50)=12750
a=12750:(1+2+3+..................+50)
a=12750:1275
a=10