#)Giải :
Bài 2 :
A = 1 + 5 + 52 + 53 + ... + 549 + 550
=> 5A = 5 + 52 + 53 + ...+ 550 + 551
=> 5A - A = 4A = ( 5 + 52 + 53 + ... + 550 + 551 ) - ( 1 + 5 + 52 + 53 + ... + 549 + 550 )
=> 4A = 551 - 1
=> A = 551 - 1 / 4
#)Giải :
Bài 1 :
a) ( x - 1/2 )2 + ( y + 1/2 )2 = 0
Ta có : ( x - 1/2 )2 ≥ 0 ; ( y + 1/2 )2 ≤ 0
=> ( x - 1/2 )2 = 0 ; ( y + 1/2)2 = 0
=> ( x - 1/2 )2 = 0 => x - 1/2 = 0 => x = 1/2
=> ( y + 1/2 )2 = 0 => y + 1/2 = 0 => y = -1/2
Vậy x = 1/2 ; y = -1/2
P/s : Maybe right ...