Mấy bài này bạn vận dụng qui tắc đổi dấu trong ngoặc và bấm máy tính bờ làm thôi

a,\(\left(57-725\right)-\left(605-53\right)\)

\(=57-725-605+53\)

\(=-1220\)

b,\(-452-\left(-67+75-452\right)\)

\(=-452+67-75+452\)

\(=-8\)

c,\(\left(55+45+15\right)-\left(15-55+45\right)\)

\(=55+45+15-15+55-45\)

\(=110\)

86/904 100%

tik cho to nhe

a) ( 725 + 275 ) : 2 = 1000:2

= 500

b) 1458 x ( 460 + 540 ) = 1458 x 1000

= 1458000

d) (120 + 112 ) + ( 116 + 84 ) = 232 + 200

= 432 

725:2+275:2=275

1458x460+1458x540=1458000

52+54+55+56+...+88=2536

120+116+112+84=432

S=(5+52+53+54+55+56)+...+(591+592+593+594+595+596)S=(5+52+53+54+55+56)+...+(591+592+593+594+595+596)

=5(1+5+52+53+54+55)+...+591(1+52+53+54+55)=5.3906+...+591.3906=3906(5+...+596)=3.126(5+...+591)=5(1+5+52+53+54+55)+...+591(1+52+53+54+55)=5.3906+...+591.3906=3906(5+...+596)=3.126(5+...+591)

chia hết cho 126

a/ =15+37+52-37-17

=(15+52)-17+(37-37)

=67-17+0

=50

b/=38-42+14-25+27+15

=-4+14+27-25+15

=10+27-40

=37-40

=-3

c/=-21+32+12-32

=-21+12+32-32

=11+0

=11

d/=-12-21+23-23+21-10

=-33+0+11

=-22

e/=57-725-605+53

=-668-605+53

=-1273+53

=-1220

f/=55+45+15-15+55-45

=55+55+45-45+15-15

=110+0+0

=110

Đặt \(A=1.3.5.7...99\)

\(B=\dfrac{51}{2}.\dfrac{52}{2}.\dfrac{53}{2}...\dfrac{100}{2}\)

Ta có:

\(A=1.3.5.7...99\)

\(\Rightarrow A=\dfrac{\left(1.3.5.7...99\right)\left(2.4.6.8...100\right)}{2.4.6.8...100}\)

\(\Rightarrow A=\dfrac{1.2.3.4...100}{2.4.6.8...100}\)

\(\Rightarrow A=\dfrac{1.2.3.4...100}{\left(2.1\right)\left(2.2\right)\left(2.3\right)...\left(2.50\right)}\)

\(\Rightarrow A=\dfrac{\left(1.2.3.4...50\right)\left(51.52.53...100\right)}{\left(1.2.3.4...50\right)\left(2.2.2.2...2\right)}\)

\(\Rightarrow A=\dfrac{51.52.53.54...100}{2.2.2.2...2}\)

\(\Rightarrow A=\dfrac{51}{2}.\dfrac{52}{2}.\dfrac{53}{2}....\dfrac{100}{2}\)

\(\Rightarrow A=B\)

Vậy \(1.3.5.7...99=\dfrac{51}{2}.\dfrac{52}{2}.\dfrac{53}{2}...\dfrac{100}{2}\) (Đpcm)

VT: 1.3.5.7....99=\(\dfrac{(1.3.5.7.....99).\left(2.4.6....100\right)}{2.4.6....100}\)

\(=\dfrac{\left(1.3.5.7.....99\right)\left(2.4.6.....100\right)}{1.2.2.2.2.3.....2.50}\)\(=\dfrac{\left(1.2.3.4.....50\right)\left(51.52.53....100\right)}{\left(1.2.3.4......50\right)\left(2.2.2.2.2....2\right)}\)

\(=\dfrac{51.52.53......100}{2.2.2.2.....2}=\dfrac{51}{2}.\dfrac{52}{2}.\dfrac{53}{2}......\dfrac{100}{2}=VP\left(đpcm\right)\)

 kết quả =-1220

phá ngoặc ta có 

57 - 725 - 605 + 53

= -668 - 605 + 53

= -1273 + 53

=-1220

(57-725)-(605-530

=  -668 - 552

=-1220

nhớ tick nha!

(57-725)-(605-53)=

(-668)-552=

-1220

tick to nha ban nhe, tick to nha ban nhe, minh dung 1000% luon, tick to di

\(215\frac{53}{171}-213\frac{52}{171}+\frac{342342}{171171}-\frac{1}{171}\)

\(=215+\frac{53}{171}-213-\frac{52}{171}+\frac{342}{171}-\frac{1}{171}\)

\(=\left(215-213\right)+\left(\frac{53}{171}-\frac{52}{171}+\frac{342}{171}-\frac{1}{171}\right)\)

\(=2+2\)

\(=4\)

Study well ! >_<

Ta thấy:

\(\dfrac{1}{51}< \dfrac{1}{50}\)

\(\dfrac{1}{52}< \dfrac{1}{50}\)

...

\(\dfrac{1}{100}< \dfrac{1}{50}\)

\(\Rightarrow\dfrac{1}{51}+\dfrac{1}{52}+...+\dfrac{1}{100}< \dfrac{1}{50}.50=1\)

\(\Rightarrow\dfrac{1}{51}+\dfrac{1}{52}+...+\dfrac{1}{100}< 1\left(1\right)\)

Lại có:

\(\dfrac{1}{51}>\dfrac{1}{100}\)

\(\dfrac{1}{52}>\dfrac{1}{100}\)

...

\(\dfrac{1}{100}=\dfrac{1}{100}\)

\(\Rightarrow\dfrac{1}{51}+\dfrac{1}{52}+...+\dfrac{1}{100}>\dfrac{1}{100}.50=\dfrac{1}{2}\)

\(\Rightarrow\dfrac{1}{51}+\dfrac{1}{52}+...+\dfrac{1}{100}>\dfrac{1}{2}\left(2\right)\)

Từ (1),(2)\(\Rightarrow\)\(\dfrac{1}{2}< \dfrac{1}{51}+\dfrac{1}{52}+...+\dfrac{1}{100}< 1\)