Question

Tìm a biết: a + a × 2 + a × 3 + a × 4 + … + a × 49 + a × 50 = 12750

Answer 1

a + a × 2 + a × 3 + a × 4 + … + a × 49 + a × 50 = 12750

a x (1 + 2 + 3 + 4 + ... + 49 + 50)  = 12750

a x 1275  = 12750

a = 12750 :1275

a = 10