Bài 4:

Chu vi hình vuông là: 8 x 4 = 32(cm)

Diện tích hình vuông là: 8 x 8 = 64 (cm2)

Bài 5:

Chu vi hình chữ nhật là:(15+8) x2=46(cm)

Diện tích hình chữ nhật là:15 x  8=120(cm2)

Bài 1:

10 x 10 = 100 

9 x 9 = 81 

8 x 8 = 64 

7 x 7 = 49 

6 x 6 = 36 

5 x 5 = 25 

4 x 4 = 16 

3 x 3 = 9 

2 x 2 = 4 

1 x 1 = 1

10 . 10 =10²=100
9 . 9 =9²=81
8 . 8 =8²=64
7 . 7 =7²=49
6 . 6 =6²=36
5 . 5 =5²=25
4 . 4 =4²=16
3 . 3 =3²=9
2 . 2 =2²=4
1 . 1 =1²=1

Áp dụng công thức tính dãy số cách đều ta có: 

1 + 2 + 3 + ... + 20

= (1 + 20) x 20 : 2

= 21 x 10

= 210

Cách 1:

Áp dụng công thức tính dãy số ta có

[(20 - 1) : 1 + 1]  x  (20 + 1) : 2     

= 20 x 21 : 2

= 10 x 21

= 210 

Cách 2 :

1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 + 13 + 14 + 15 + 16 + 17 + 18 + 19 + 20

= (20 +1 ) + (19 + 2) +....+ (11+ 10)

= 21 + 21 + ....+ 21  ( 10 số 21)

= 21 x 10 

= 210

câu D đúng.

vì 36 = 6 + 6 + 6 + 6 x 3.

tick mik nha

Số số hạng của dãy số là:

10-0+1=11(số)

Tổng của dãy số là: \(\left(10+0\right)\times\frac{11}{2}=10\times\frac{11}{2}=5\times11=55\)

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Lý thuyết:

- Khi nhân một số với 0 ta được kết quả cũng bằng 0.

- Khi 0 chia cho một số ta được kết quả cũng bằng 0

Câu số 1:

    ( 18 - 9 x 2 ) x ( 2 + 4 + 6 + 8 + 10 )

   =      0         x  ( 2 + 4 + 6 + 8 + 10 )

   =                 0

Câu số 2:

    ( 7 x 8 - 56 ) : ( 2 + 4 + 6 + 8 + 112 )

   =       0          : ( 2 + 4 + 6 + 8 + 112 )

   =                  0

Câu số 3:

    ( 2 + 125 + 6 + 145 + 112 ) x ( 42 - 6 x 7 )

   = ( 2 + 125 + 6 + 145 + 112 ) x       0

   =                                            0

Câu số 4:

    ( 12 x 6 - 12 x 4 - 12 x 2 ) x ( 347 + 125 )

   =      ( 12 x 6 - 12 x 6 )       x ( 347 + 125 )

   =                   0                   x ( 347 + 125 )

   =                                       0

Câu số 5:

    ( a x 7 + a x 8 - a x 15 ) : ( 1 + 2 + 3 + ... + 10 )

   =     ( a x 15 - a x 15 )     : ( 1 + 2 + 3 + ... + 10 )

   =               0                    : ( 1 + 2 + 3 + ... + 10 )

   =                                     0

Câu số 6:

    58 - 58 x ( 6 + 54 - 60 )

  = 58 - 58 x        0

   = 58 -       0

   = 58

Câu số 7:

    32 + 63 x a x ( a x 1 - a : 1 ) + 32 x 8 + 32

   = 32 + 63 x a x        0             + 32 x 8 + 32

   = ( 32 + 32 x 8 + 32 ) + 63 x a x 0

   =       ( 32 x 10 )          + 0

   =                         320

[(1+9)+(2+8)+(3+7)+(4+6)+5]x2

=(10+10+10+10+5)x2

=45x2

=90

50x2+2x10

=2x(50+10)

=2x60

=120

\(x = {-b \pm \sqrt{b^2-4ac} \over 2a}\)

giúp tôi nhé\(x = {-b \pm \sqrt{b^2-4ac} \over 2a}\)cái này bấm nhầm

Câu 1 : 46 + 178 = 224

Câu 2 : 38 + 895 = 933

Câu 3 : 216 - 188 = 28

Câu 4 : 251 - 67 = 184

Câu 5 : 21 x 2 : 7 = 6

Câu 6 : 24 : 2 x 4 = 48

Câu 7 :

32 : X = 8

       X = 32 : 8 

       X = 4

Vậy X bằng : 4

Câu 8 : 

21 : X = 3 

       X = 21 : 3

       X = 7

Vậy X bằng : 7

Câu 9 : 

24 : X = 2 + 6 

24 : X = 8

       X = 24 : 8

       X = 3

Vậy X bằng : 3

Câu 10 : 

56 : X = 14 : 2

56 : X = 7

       X = 56 : 7

       X = 8

Vậy X bằng : 8

TK nhé

1: Tìm x

a,  x + 65 = 21

            x = 21 - 65

            x = -44

b, 12 - x = 30

           x = 12 - 30

           x = -18

2) Tính nhanh

SSH : (9-1):1+1= 9 ( số)

TBC:   (9+1):2 = 5]

Tổng là: 9 * 5 = 45

1, tìm x

a, x+ 65 = 67 - 56

=> x + 65 =  11

=> x= -54

vậy x= -54

b, 12 -x =5 x 6

=> 12 - x =30

=> x=-18

vậy x=-18

2, tính nhanh

1+2+3+4+5+6+7+8+9=(1+9)+(2+8)+(3+7)+(4+6)+5

=10 + 10+ 10+ 10+ 5=45

Bài 1:

Bài 2: