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...

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

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

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

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

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

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

a: \(\left(-305\right)+400+305\)

\(=\left(-305+305\right)+400\)

=0+400

=400

b: \(\left(-511\right)-\left(-11\right)\)

=-511+11

=-(511-11)

=-500

c: \(0-\left(12345+15\right)\)

\(=0-12360\)

=-12360

d: \(333-\left[\left(-14657\right)+57\right]-78\)

\(=333+14657-57-78\)

\(=\left(333-78\right)+14600\)

\(=255+14600=14855\)

a) $371+731-271-531$

$=(371-271)+(731-531)$

$=100+200$

$=300$

b) $57+58+59+60+61-17-18-19-20-21$

$=(57-17)+(58-18)+(59-19)+(60-20)+(61-21)$

$=40+40+40+40+40$

$=40\cdot5$

$=200$

c) $9-10+11-12+13-14+15-16$

$=(9-10)+(11-12)+(13-14)+(15-16)$

$=-1+(-1)+(-1)+(-1)$

$=-1\cdot4$

$=-4$

$\text{#}Toru$

thanks

a: \(145+43+\left(-145\right)+57\)

\(=\left(145-145\right)+\left(43+57\right)\)

=0+100

=100

b: \(\left(-123\right)+101+\left(-777\right)+99\)

\(=\left(-123-777\right)+\left(101+99\right)\)

=-900+200

=-700

c: \(\left(-8955\right)+33+\left(-45\right)+\left(-133\right)\)

\(=\left(-8955-45\right)+\left(33-133\right)\)

\(=\left(-9000\right)+\left(-100\right)=-9100\)

d: \(\left(-2\right)+\left(-4\right)+\left(-6\right)+\left(-8\right)+\left(-10\right)+8+10+12\)

\(=\left(12-2\right)+\left(-4-6\right)+\left(-8+8\right)+\left(-10+10\right)\)

=10-10+0+0

=0

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

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

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