A=[57(157-99-57)]:57+57= 57:57+57=58

mk hoc roi muon minh giai tick  nha

A=(157.57-99.57-57²):57+57

A = 1 + 57 

A = 58

B=1.2+2.3+3.4+............+n.(n+1)

B = 1.2+2.3+3.4+.............+n(n+1) 

=1(1+1) + 2(2+1) + 3(3+1) +...+n(n+1) 
=(1^2 + 2^2 + 3^2 +...+ n^2) + (1 + 2 + 3 + ...+ n) 
ta có các công thức: 
1^2 + 2^2 + 3^2 +...+ n^2 = n(n+1)(2n+1)/6 
1 + 2 + 3 + ...+ n = n(n+1)/2 
thay vào ta có: 
S = n(n+1)(2n+1)/6 + n(n+1)/2 
=n(n+1)/2[(2n+1)/3 + 1] 
=n(n+1)(n+2)/3

\(A=\left(157.57-99.57-57^2\right):57+57\)

\(=\left[\left(157-99\right).57-57^2\right]:57+57\)

\(=\left[58.57-57^2\right]:57+57\)

\(=\left[3306-3249\right]:57+57\)

\(=57:57+57\)

\(=1+57=58\)

Vậy....

\(B=\left[160.\left(730-700\right):2^4-4^2\right].13\)

\(=\left[160.30:16-16\right].13\)

\(=\left[4800:16-16\right].13\)

\(=\left(300-16\right).13\)

\(=284.13=3692\)

Vậy...

\(C=\left(3^2.17+3^2.38-55\right):\left(2^3.68-2^3.13\right)\)

\(=\left(9.17+9.38-55\right):\left(8.68-8.13\right)\)

\(=\left[9.\left(17+38\right)-55\right]:\left[8.\left(68-13\right)\right]\)

\(=\left[9.55-55\right]:\left[8.55\right]\)

\(=\left[8.55\right]:\left[8.55\right]\)

\(=1\)

Vậy...

\(D=2.51^2:17^2+\left(8.5^2-2^4-3^2\right):56+2009\)

\(=2.8+\left(8.25-16-9\right):56+2009\)

\(=18+\left(200-16-9\right):56+2009\)

\(=18+175:56+2009\)

\(=18+\dfrac{25}{8}+2009\)

\(=\dfrac{16241}{8}\)

=57.(157-98-57):57 (bn đặt thừa số chung nhé)

=157-98-57=2 (sai thôi nhé mk ko bấm máy)

=\(=\frac{57\left(157-98-57\right)}{57}=2\)

a: =-48+27+56-48-27-36

=-96+20

=-76

b: =23-57+57-33=-10

c: =-98+12-159-12-41

=-98-200

=-298

Cảm ơn bạn 

\(A=\left(157\cdot57-99\cdot57-57^2\right):57+57\)

\(A=\left(157\cdot57-99\cdot57-57\cdot57\right):57+57\)

\(A=57\cdot\left(157-99-57\right):57+57\)

\(A=57:57+57\)

\(A=1+57\)

\(A=58\)

\(B=2-4+6-8+...+98-100\)

\(B=\left(2-4\right)+\left(6-8\right)+...+\left(98-100\right)\)(25 cặp)

\(B=-2\cdot25\)

\(B=-50\)

Hơi trễ :))

C

khi bỏ dấu ngoặc biểu thức 120+(-8)-(42-57) ta được:

A.120+8-42-57

B.120-8-42-57

C.120-8-42+57

D.120+8-42+57