Question

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

Answer 1

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

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

Tổng trong ngoặc=[50x(50+1)]:2=1275

=>a=12750:1275=10

 vậy a=10

Answer 2

10

làm bạn mình nha

Answer 3

a + a x 2 + a x 3 + a x 4 + ..... + a x 49 + a x 50 = 12750

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

a x 1275                           = 12750

a                                      = 12750 : 1275

a                                      = 10

Answer 4

\(a+a\times2+a\times3+a\times4+...+a\times49+a\times50=12750\)

\(a\times\left(1+2+3+...+50\right)=12750\)

\(a\times1257=12750\)

\(a=12750\div1275\)

\(a=10\)