idonno

giupminhdi

6.(5x + 35) = 330

5x + 35 = 55

5x = 20 

x = 4 

6.(5x+35)=330

    5x+35 =330:6

    5x+35 =  55

    5x       = 55-35

    5x       =  20

      x       = 20:5

      x       =   4

6x(5x+35)=330

    5x+35=330:6

    5x+35=55

         5x=55-35

         5x=20

          x=4

k cho minh nha

-472 + (235 - 28) - 35 - 350

= -472 + 207 - 35 - 350

= -265 - 35 - 350

= 300 - 350 = -50

-50

bằng -650

b,x²-2x-35=0

=>(x²-2x+1)-36=0

=>(x-1)²-6²=0

=>(x-1-6)(x-1+6)=0

=>(x-7)(x+5)=0

=>x=7 hoặc x=-5

21.{350 : [274 - 2³(35 - 28 : 4)]}
= 21.{350 : [274 - 8(35 - 7)]}
= 21.{350 : [274 - 8.28]}
= 21.{350 : [274 - 224]}
= 21.{350 : 50}
= 21.7
= 147

21.{350:[274-2³.(35-28:4)

=21.{350:[274-8.28]

=21.{350:[274-224]

=21.{350:50}

=21.7=147

\(đk:x\ne1\\ \dfrac{x^2+5x}{3x^2-6x+3}:\dfrac{7x+35}{6x-6}\\ =\dfrac{x\left(x+5\right)}{3\left(x^2-2x+1\right)}:\dfrac{7\left(x+5\right)}{6\left(x-1\right)}\\ =\dfrac{x\left(x+5\right)}{3\left(x-1\right)^2}\times\dfrac{6\left(x-1\right)}{7\left(x+5\right)}\\ =\dfrac{2x}{7\left(x-1\right)}\)

`Answer:`

\(S=\frac{1}{14}+\frac{1}{35}+\frac{1}{65}+...+\frac{1}{350}\)

\(\Rightarrow S=\frac{2}{28}+\frac{2}{70}+\frac{2}{130}+...+\frac{2}{700}\)

\(\Rightarrow S=\frac{2}{4.7}+\frac{2}{7.10}+\frac{2}{10.13}+...+\frac{2}{25.28}\)

\(\Rightarrow S=\frac{2}{3}\left(\frac{1}{4.7}+\frac{1}{7.10}+\frac{1}{10.13}+...+\frac{1}{25.28}\right)\)

\(\Rightarrow S=\frac{2}{3}\left(\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+...+\frac{1}{25}-\frac{1}{28}\right)\)

\(\Rightarrow S=\frac{2}{3}.\frac{3}{14}\)

\(\Rightarrow S=\frac{1}{7}\)

nhầm  28:4

tự tính đi dễ mà

21.{350:[274-2³(35-2:4)]}

=21.{250:[274-8.34,5]}

=21.{250:(-2)}

=21.(-125)

=-2625

a: -127+208-73+92

\(=\left(-127-73\right)+\left(208+92\right)\)

\(=300-200=100\)

b: \(-46+391+246-691\)

\(=\left(-46+246\right)+\left(391-691\right)\)

\(=200-300=-100\)

c: \(-472+\left(235-28\right)-\left(35-350\right)\)

\(=-472+235-28-35+350\)

\(=\left(-472-28\right)+350+\left(235-35\right)\)

\(=-500+350+200=50\)

a) -127+208-73+92

b) 

c)