Question

tim a biet a+a*2+a*3+a*4....+a*49+A*50=12750

Answer 1

a + 2a + 3a +...+ 50a = 12750

=> a(1 + 2 + 3 +...+ 50) = 12750

=> 1275a = 12750

=> a = 10

Answer 2

a+2a+3a+4a+..+50a=12750

<=>(1+2+3+4+..+50).a=12750

<=>\(\left[\frac{50.\left(50+1\right)}{2}\right].a=12750\Rightarrow1275.a=12750\)

<=>a=10

Vậy a=10