a,35x34+35x86+65x75+65x45

=35x(34+86)+65x(75+45)

=35x120+65x120

=120x(35+65)

=120x100

=12000

b,3x25x8+4x37x6+2x38x12

=(3x8)x25+(4x6)x37+(2x12)x38

=24x25+24x37+24x38

=24x(25+37+38)

=24x(62+38)

=24x100

=2400

c,12x53+53x172-53x84

=53x(12+172-84)

=53x(184-84)

=53x100

=5300

a.35x(34+86)+65x(75+45)=35x120+65x120=120x(35+65)=120x100=12000

b.3x25x8+4x37x6x2x38x12=24x25+24x37+24x38=24x(25+37+38)=24x100=2400

c.53x(12+172-84)=53x100=5300

(-0,4)x(-0,5)x(-0,8)

= 0,2x(-0,8)

=-0,16 

\(=-375\left(69+31\right)=-375\cdot100=-37500\)

Ta có: \(A=1+\dfrac{1}{8}+\dfrac{1}{24}+\dfrac{1}{48}+\dfrac{1}{80}+\dfrac{1}{120}\)

\(\Leftrightarrow2A=2+\dfrac{2}{2\cdot4}+\dfrac{2}{4\cdot6}+\dfrac{2}{6\cdot8}+\dfrac{2}{8\cdot10}+\dfrac{2}{10\cdot12}\)

\(\Leftrightarrow2A=2+\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{10}+\dfrac{1}{10}-\dfrac{1}{12}\)

\(\Leftrightarrow2A=2+\dfrac{1}{2}-\dfrac{1}{12}\)

\(\Leftrightarrow2A=\dfrac{24}{12}+\dfrac{6}{12}-\dfrac{1}{12}\)

\(\Leftrightarrow2A=\dfrac{29}{12}\)

hay \(A=\dfrac{29}{24}\)

A=1+1/2+1/3+1/6+(1/12+1/15+1/20+1/30)+1/35

=71/35+7/30=95/42

a) \(1+2+3+...+2021=\dfrac{\left(2021+1\right)\left(\dfrac{2021-1}{1}+1\right)}{2}=2043231\)

b) Giống a

c) \(11+13+15+...131=\dfrac{\left(131+11\right)\left(\dfrac{131-11}{2}+1\right)}{2}=4331\)

ải b luôn đi

a: \(2\cdot53\cdot12+4\cdot6\cdot87-3\cdot8\cdot40\)

\(=24\left(53+87-40\right)\)

=2400

b: \(5\cdot7\cdot77+7\cdot60+49\cdot25-45\cdot42\)

\(=35\cdot77+35\cdot12+49\cdot25-45\cdot42\)

\(=35\cdot89+35\left(7\cdot5-9\cdot6\right)\)

\(=35\cdot70=2450\)

a) 2.53.12+4.6.87-3.8.40

=24.53+24.87-24.40

=24.(53+87-40)

=24.100

=2400

b) 5.7.77-7.60+49.25-45.42

=5.7.77-7.60+7.7.25-45.6.7

=7.(5.77-60+7.25-6.45)

=7.230

=1610

Bài 2: 

a: =>x-35=-23

=>x=12

b: =>|x-8|=13

=>x-8=13 hoặc x-8=-13

=>x=21 hoặc x=-5

Bài 1: 

a: =42-98-42+12-12=-98

b: =10x4x3x(-25)=40x(-25)x3=-1000x3=-3000

 (-4).(+3).(-125).(-8)=-12000

b) (-67).(1-301)-301.67= -67

ko phải tính đáp án ra luôn nếu ra luôn thì mik có máy tính