Question

f 17+(-20)+23+(-26)+...+53+(-56)

Answer 1

17 + ( -20 ) + 23 + ( -26 ) + ... + 53 + ( -56 )

= [ 17 + ( -20 )] + [ 23 + ( -26 )] + ... + [ 53 + ( -56 )] có 7 nhóm

= ( -3 ) . 7

= -21

Answer 2

(x+1)+(x+2)+(x+3)+(x+4)+.....+(x + 56)=14700:5