Question

1+3+5+...+(2x-1)=225

Answer 1

1 + 3 + 5 + ... + ( 2x - 1 ) = 225

1 + 3 + 5 + ... + ( 2x -1 ) = [ ( 1 + 2x  - 1 ) x ] : 2 = x²

Ta có : x² = 225 

x² = 3² x 5² = ( 3 x 5 )² = 15² 

 => x = 15

Vậy x = 15

Answer 2

ok bài nầy quá khó