Tính nhanh: 1+2+3+4+5+6+7-1+2+3+4+5+6+7 = 0

1+2+3+4+5+6+7-1+2+3+4+5+6+7

=(1+2+3+4+5+6+7)-(1+2+3+4+5+6+7)

Ve 1 bang ve 2=>ve 1 - ve 2= 0

Dap an bang 0

Bài 2

48 : 6 = 8

6 x 4 = 24

54 : 6 = 9

Bài 3

x x 6 = 54

x = 54 : 6

x = 9

BÀI 1;4: tương tự nhé

1 - 2 + 3 - 4 + 5 - 6 + 7 - 8 + 9

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

= 1 + 1 + 1 + 1 + 1

= 1 x 5

= 5

5

Đề có sai không bạn, mình thấy đề là \(\frac{2}{3}\times\frac{4}{5}+\frac{2}{3}\times\frac{1}{6}\)như vậy đúng hơn

10+9-8+7-6+5-4+3-2+1-0

= 10 +[(9 - 8) + (7 - 6) + (5 - 4) + (3 - 2) + (1 - 0)]

= 10 + [1 + 1 + 1 + 1 + 1]

= 10 + 1 x 5

= 10 + 5

= 15

15

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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1+2+3+4+5+6+7+8+9+10+11=66

1+2+3+4+5+6+7+8+9+10+11=66

(1+2+3+4+5+6+7+8+9.0).(9.0)

=(1+...+8+9.0)x0

=0

=36 

  HOK TỐT 

              NHA BN 

1+2+3+4+5+6+7+8+9

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

=10+10+10+10+5

=45

123+546+789=1458

Chúc bạn học giỏi!!!

Nhớ k nha vì mik làm xong đầu đó

máy tính đâu

[(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

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