coi lại câu a

1.1+1.1+1.1+1.1+1.1/1.1+1.1+9.3+6.8+.2

=33

tách ra bn

khó nhìn quá:V

1+2+3+4+5+6+7+8+9+10+11+12+13-1-2-3-4-5-6-7-8-9-10-11-12

=(1-1)+(2-2)+(3-3)+(4-4)+(5-5)+(6-6)+(7-7)+(8-8)+(9-9)+(10-10)+(11-11)+(12-12)+13

=  0  +  0  +  0  +  0  +   0  +  0  +  0  +  0  +  0  + 0  + 0   +  0  +  13

=                                 13

1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 + 13 - 1 - 2 - 3 - 4 - 5 - 6 - 7- 8 - 9 - 10 

= (1+12) + (2+11) + (3+10) + ( 4+9) + (5+8) + (6+7) + 13 -  (1+11) - ( 2+10) - ( 3+9) - (4+8) - (5+7) + 6 + 12

= 13 * 7 - 12 * 6 + 6

= 13

Ai k mk mk k lại

115/103

a) 5 – 4 – 3 – 2 – 1 + 11 + 12 + 13 + 14 + 15

= (5 + 15) + (14 – 4) + (13 – 3) + (12 – 2) + (11 – 1)

= 20 + 10 + 10 + 10 + 10

= 60 

b) 1 – 2 + 3 – 4 + 5 – 6 + 7 – 8 + 9 – 10 +11

= (1 + 3 + 5 + 7 + 9 + 11) – 2 – 4 – 8 – 10

= 36 – 24

= 12

a) 5 – 4 – 3 – 2 – 1 + 11 + 12 + 13 + 14 + 15

= (5 + 15) + (14 – 4) + (13 – 3) + (12 – 2) + (11 – 1)

= 20 + 10 + 10 + 10 + 10

= 60 

b) 1 – 2 + 3 – 4 + 5 – 6 + 7 – 8 + 9 – 10 +11

= (1 + 3 + 5 + 7 + 9 + 11) – 2 – 4 – 8 – 10

= 36 – 24

= 12

Nhân nghịch đảo - phân phối- rút gọn

P=(2/3 -1/4+5/11):(5/12+1-7/11)

P=(88/132-33/132+60/132):(55/132+132/132-84/132)

P=115/132:103/132

P=115/103

Đặt \(A=\frac{\frac{2}{3}-\frac{1}{4}+\frac{5}{11}}{\frac{5}{12}+1-\frac{7}{11}}\)

\(A=\frac{\frac{44}{132}-\frac{33}{132}+\frac{60}{132}}{\frac{55}{132}+\frac{132}{132}-\frac{84}{132}}\)=\(\frac{\frac{44.1}{132}+-\frac{33.1}{132}+\frac{60.1}{132}}{\frac{55.1}{132}+\frac{132.1}{132}-\frac{84.1}{132}}\)

\(A=\frac{\frac{1}{132}.\left(44-33+60\right)}{\frac{1}{132}.\left(55+132-84\right)}\)=\(\frac{\frac{1}{132}.71}{\frac{1}{132}.103}\)

\(A=\frac{71}{103}\)

bạn ấy sai chỗ quy đồng buoc hai ý phải là 88/132

A=(2+3+...+13)-(1+2+...+12)=2+3+...+13-1-2-...-12=(13-1)+(2-2)+(3-3)+...+(12-12)=12

12 nha cậu .