1/4 x 12/13 + 1/6 x 12/13 + 1/8 x 12/13

= 12/13 x (1/4 + 1/6 + 1/8 )

= 12/13 x 13/14

= 1/2

1/4 x 12/13 + 1/6 x 12/13 + 1/8 x 12/13= 0.5

hok tốt

12/13x(1/4+1/6+1/8)=12/13x13/24=12/24=1/2

9/13 x 7/12 + 9/13 x 5/12 - 9/13

= 9/13 x (7/12 + 5/12 - 1)

= 9/13 x 0

= 0

4/13 x 5/12 + 4/13 x 7/12 - 4/3

= 4/13 x (5/12 + 7/12) - 4/3

= 4/13 x 1 - 4/3

= 4/13 - 4/3

= -40/39

a) 9/13 x 7/12 + 9/13 x 5/12 - 9/13

= 9/13 x ( 5/12 + 7/12 - 1 )

= 9/13 x 0

= 0

b) 4/13 x 5/12 + 4/13 x 7/ 12 - 4/3

= 4/13 x ( 5/12 + 7/12 - 13/3 )

= 4/13 x ( - 10/3 )

= -40/39 

a) \(\frac{9}{13}\cdot\frac{7}{12}+\frac{9}{13}\cdot\frac{5}{12}-\frac{9}{13}\)

\(=\frac{9}{13}.\left(\frac{7}{12}+\frac{5}{12}-1\right)=\frac{9}{13}.\left(1-1\right)=\frac{9}{13}.0=0\)

b) \(\frac{4}{13}\cdot\frac{5}{12}+\frac{4}{13}\cdot\frac{7}{12}-\frac{4}{3}\)

\(=\frac{4}{13}.\left(\frac{5}{12}+\frac{7}{12}\right)-\frac{4}{3}=\frac{4}{13}.1-\frac{4}{3}=\frac{4}{13}-\frac{4}{3}\)

A

Chọn A

B

b

b

x=-2 nha bạn Cá là có trong violympic

\(\Rightarrow\frac{x+2}{10^{10}}+\frac{x+2}{11^{11}}-\frac{x+2}{12^{12}}-\frac{x+2}{13^{13}}=0\)

\(\Rightarrow\left(x+2\right)\left(\frac{1}{10^{10}}+\frac{1}{11^{11}}-\frac{1}{12^{12}}-\frac{1}{13^{13}}\right)=0\)

Vì \(\frac{1}{10^{10}}+\frac{1}{11^{11}}-\frac{1}{12^{12}}-\frac{1}{13^{13}}\ne0\)

=>x+2=0

=>x=-2

Vậy x=-2

a) 35 x 12 + 65 x 13

= 35 x 12 + 65 x (12+1)

=35 x 12 + 65 x 21 + 65

=12 x (65 + 35) + 65

= 12 x 100 + 65

= 1200 + 65

= 1265

b) (37 x 13 -13) : (24 + 37 x 12)

= [ 37 x (12+1) - 13 ] :  (24 + 37 x 12)

=( 37 x 12 + 37 - 13) : ( 24 +37 x 12)

=( 37 x 12 +24) : (24 + 37 x 12)

=\(1\)

Ta có nhận xét phần b hai tích chia cho nhau mà 2 tích giống nhau vậy kết quả là \(1\)

35 x 12 + 65 x 13 = 1265

( 37 x 13 - 13) : (24 + 37 x 12) = 1

a) 35 x 12 + 65 x 13 = 420 + 845

                              = 1265

b) ( 37 x 13 - 13 ) : (24 + 37 x 12) = 468 : 468

                                                 = 1

=>

\(\frac{x+2}{10^{10}}+\frac{x+2}{11^{11}}-\frac{x+2}{12^{12}}-\frac{x+2}{13^{13}}=0\)

=>\(\left(x+2\right).\left(\frac{1}{10^{10}}+\frac{1}{11^{11}}-\frac{1}{12^{12}}-\frac{1}{13^{13}}=0\right)\)

vì \(\frac{1}{10^{10}}>\frac{1}{11^{11}}>\frac{1}{12^{12}}>\frac{1}{13^{13}}=>\frac{1}{10^{10}}+\frac{1}{11^{11}}-\frac{1}{12^{12}}-\frac{1}{13^{13}}\ne0\)

=>x+2=0

=>x=-2

tick nhé

\(\frac{x+2}{10^{10}}+\frac{x+2}{11^{11}}=\frac{x+2}{12^{12}}+\frac{x+2}{13^{13}}\)

\(=>\frac{x+2}{10^{10}}+\frac{x+2}{11^{11}}-\frac{x+2}{12^{12}}-\frac{x+2}{13^{13}}=0\)

\(=>\left(x+2\right).\left(\frac{1}{10^{10}}+\frac{1}{11^{11}}-\frac{1}{12^{12}}-\frac{1}{13^{13}}\right)=0\)

Vì \(\frac{1}{10^{10}}>\frac{1}{11^{11}}>\frac{1}{12^{12}}>\frac{1}{13^{13}}\)

Nên \(\frac{1}{10^{10}}+\frac{1}{11^{11}}-\frac{1}{12^{12}}-\frac{1}{13^{13}}\)khác 0

Suy ra:  x+2=0

             x   =0 - 2

             x = -2

                              TICK NHA

x=11 suy ra 12=x+1 thay vào A ta có:

A=x^17- (x+1)x^16 + (x+1)x^15 - (x+1)x^14 + .....- (x+1)x^2+(x+1)x -1

= x^17 - x^17 -x^16 + x^16 + x^15 - x^15 - x^14 +.....- x^3 -x^2 + x^2 +x -1

= x-1= 11-1=10

*cam tớ hơi mờ nên thông cảm nhé:<.

\(\dfrac{12}{1\cdot5}+\dfrac{12}{5\cdot9}+...+\dfrac{12}{97\cdot101}\)

\(=3\left(\dfrac{4}{1\cdot5}+\dfrac{4}{5\cdot9}+...+\dfrac{4}{97\cdot101}\right)\)

\(=3\left(1-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{9}+...+\dfrac{1}{97}-\dfrac{1}{101}\right)\)

=3*100/101

=300/101