Question

 

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

Ti`m a

Answer 1

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

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

đặt S=1+2+3+...+50

=>S=(50+1) x 50 : 2 = 1275

=> a x S = 12750

=> a x 1275 = 12750

=> a = 10

vậy a=10

Answer 2

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

1+2+3+...+50=1275

a=10