a) 21.7²-11.7²+90.7²+49.125.16

=21.7²-11.7²+90.7²+7².2000

=7².(21-11+90+2000)

=7².2100

=49.2100

=102900

a) \(21\cdot7^2-11\cdot7^2+90\cdot7^2+7^2\cdot125\cdot16=7^2\cdot\left(21-11+90+125\cdot16\right)=7^2\cdot2100=102900\)

\(21.7^2-11.7^2+90.7^2+49.125.16\)

=\(21.7^2-11.7^2+90.7^2+7^2.2000\)

=\(7^2.\left(21-11+90+2000\right)\)

=\(7^2.2100\)

=\(102900\)

a) 35× 34 +35× 86 + 65 × 75 + 65× 45

= 35× ( 34+86) + 65× (75 + 45)

= 35× 120 + 65 × 120

= 120 × ( 35 + 65)

= 120 × 100 = 12000

a) 35.34 + 35.86 + 65.75 + 65.45

= 35. ( 34 + 86 ) + 65 . ( 75 + 25 ) 

= 35 . 120 + 65 . 100

= 4200 + 6500

= 10700

b) 21.49 - 11.49 + 90.49 + 49.125.16

= 49 . ( 21-11+90) +49 .125.8.2

= 49 .100 + 49 .1000 .2

= 4900 + 49000 .2

= 4900 + 98000

= 102900

Hên xui nhé !!!

Bạn Bích Trâm sai đề bài câu a rùi

Đáp án đúg là 12480

35.34+35.86+65.75+65.45=35.(34+86)+65.(75+45)=35.120+65.120=100.120=12000

a)

\(\Rightarrow35.\left(34+86\right)+65.\left(75+45\right)\)

\(\Rightarrow35.120+65.120\)

\(\Rightarrow120.\left(35+65\right)=120.100=12000\)

b)

\(\Leftrightarrow21.49-11.49+90.49+49.125.16\)

\(\Rightarrow49.\left(21-11+90+2000\right)\)

\(\Rightarrow49.2100=102900\)

a) 35 . 34 + 35 . 86 + 65 . 75 + 65 . 45
= 35 . ( 34 + 86 ) + 65 . ( 75 + 45 )
= 35 . 120 + 65 . 120
= ( 35 + 65 ) . 120
= 100 . 120
= 12000

b) 21 . 7² - 11 . 7² + 90 . 7² + 49 . 125 . 16
= 21 . 49 - 11 . 49 + 90 . 49 + 49 . 125 . 16
= ( 21 - 11 + 90 ) . 49 + 49 . 125 . 8 . 2
= 100 . 49 + 49 . 2 . 1000
= 100 . 49 + 49 . 2000
= ( 100 + 2000 ) . 49
= 2100 . 49
= 102900

a) 35.34 + 35.86 + 65.75 + 65.45 =

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

100 x 120 x 120

100 x 14400

1440000

\(35\cdot34+35\cdot86+65\cdot75+65\cdot45\\ =35\cdot\left(34+86\right)+65\cdot\left(75+45\right)\\ =35\cdot120+65\cdot120\\ =120\cdot\left(35+65\right)\\ =120\cdot100\\ =12000\)

=202,35 tk m nhé

=202.35

35.34 + 35.86 + 65.75 + 65.4

= 35.(34+86) + 65.(75+4)

= 35.120 + 65.79

= 3840 + 5135

= 8975

Xét\(3A=1\cdot2\left(3-0\right)+2\cdot3\left(4-1\right)+\cdot\cdot\cdot+99\cdot100\left(101-98\right)\)

     \(3A=1\cdot2\cdot3-0\cdot1\cdot2+2\cdot3\cdot4-1\cdot2\cdot3+...+99\cdot100\cdot101-98\cdot99\cdot100\)

     \(3A=99\cdot100\cdot101\)

\(\Rightarrow A=33\cdot100\cdot101=30300\)

A = 1 . 2 + 2 . 3 + 3 . 4 + ... + 99 . 100

3A = 1 . 2 . 3 + 2 . 3 . 3 + 3 . 4 . 3 + ... + 99 . 100 . 3

3A = 1 . 2 . ( 3 - 0 ) + 2 . 3 . ( 4 - 1 ) + 3 . 4 . ( 5 - 2 ) + ... + 99 . 100 . ( 101 - 98 )

3A = 1. 2 . 3 - 0 . 1 . 2 6 2 . 3 . 4 - 1 . 2 . 3 + 3 . 4 . 5 + 2 . 3 . 4 + ... + 99 . 100 . 101 - 98 . 99 . 100

3A = ( 1 . 2 . 3 - 1 . 2 . 3 ) + ( 2 . 3 . 4 - 2 . 3 . 4 ) + ... + ( 98 . 99 . 100 - 98 . 99 . 100 ) + ( 99 . 100 . 101 - 0.1 . 2 )

3A = 0 + 0 + 0 + ... + 0 + 99 . 100 . 101 - 0 . 1 . 2

3A = 99 . 100 . 101 - 0

A = \(\frac{99\cdot100\cdot101}{3}=333300\)

\(35\cdot34+35\cdot86+65\cdot75+65\cdot45=35\left(34+86\right)+65\left(75+45\right)\)

                                                                              \(=35\cdot120+65\cdot120\)

                                                                                \(=120\left(35+65\right)\)

                                                                                \(=120\cdot100=12000\)

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