Question

Bài 1:

a) A= 1-2+3-4+5-6+...+99-100

b) B=1+2-3-4+5+6-7-8+9+10-11-12+...+97+98-99-100

Answer 1

a) A= 1-2+3-4+5-6+...+99-100

A = ( 1 - 2 ) + ( 3 - 4 ) + ( 5 - 6 ) + ... + ( 99 - 100 )               ( có 50 cặp )

A = ( - 1 ) + ( -1 ) + ( -1 ) + ,.. + ( -1 )

A = ( - 1 ) . 50

A = -50

b) B = 1 + 2 - 3 - 4 + 5 + 6 - 7 - 8 + 9 + 10 - 11 - 12 + ... + 97 + 98 - 99 - 100

B = ( 1 + 2 - 3 - 4 ) + ( 5 + 6 - 7 - 8 ) + ( 9 + 10 - 11 - 12 ) + ... + ( 97 + 98 - 99 - 100 )            ( có 25 cặp )

B = ( - 4 ) + ( - 4 ) + ( - 4 ) + ... + ( - 4 )

B = ( - 4 ) x 25 

B = -100