(-72).(34 - 12) - 34.(12 - 72)

=   -72.34 + 72.12 - 34.12 + 34.72

=(-72.34 + 34.72)  + (72.12 - 34.12)

= 0 + 12.(72 - 34)

= 12. 38

= 456

1 2 + − 1 2 + − 2 3 + 2 3 + 3 4 + − 3 4 + − 4 5 + 4 5 + 5 6 + − 5 6 = 0

1 2 + − 1 2 + − 2 3 + 2 3 + 3 4 + − 3 4 + − 4 5 + 4 5 + 5 6 + − 5 6 = 0

Đây nha

a)-900

b)456

a) (43 -13).(-3) +27.(-14 - 16) = -900

b) (-72).(34 -12) -34.(12 - 72) = 456

a . 2 5     +     3 4 = 8 20 + 15 20 = 23 20

b .   2 5 + 3 10 - 1 2 = 4 10 + 3 10 - 1 2 = 7 10 - 1 2 = 7 10 - 5 10 = 2 10 = 1 5

c . 8 11 + 8 33 × 3 4 = 8 11 + 24 132 = 8 11 - 2 11 = 6 11

12. 68 + 34. 18 - 34- 142

=12.2.34+34.18+108

=24.34+34.18+108

=34.(24+18)+108

=34.42+108

=1428+108

=1536

3:

a: (a-b+c)-(c-b-a)

=a-b+c-c+b+a

=2a

b: \(-\left(a-b\right)+\left(b-c+a\right)-\left(a+b-c\right)\)

\(=-a+b+b-c+a-a-b+c\)

\(=b-a\)

c: \(-\left(a-b-c\right)-\left(-a+b+c\right)-\left(a-b+c\right)\)

\(=-a+b+c+a-b-c-a+b-c\)

\(=-a+b-c\)

2:

a: \(12-\left(-12\right)=12+12=24\)

b: \(-\left(35-49\right)+\left(27-49\right)=-35+49+27-49\)

=-35+27

=-8

c: \(47-\left(59-63\right)+\left(63-47\right)\)

\(=47-59+63+63-47\)

=126-59

=67

d: \(-\left(-20\right)-\left(-30\right)-70\)

=20+30-70

=50-70

=-20

12 + 21 x 12 + 12 x 34

= 12 x ( 1 + 12 + 34 )

= 12 x 45

= 540

12 + 21 x 12 + 12 x 34

= 12 x 1 + 21 x 12 + 12 x 34

= 12 x (1+21+34)

= 12 x 56

= 672

A

Bài 7. Tính nhanh giá trị biểu thức: 34 × 12 + 34 × 7 – 34 × 9:

C. 2400

D. 3210

B. 3400

A. 340

a) 5 13 + − 5 7 + − 20 41 + 8 13 + − 21 41 = 5 13 + 8 13 + − 20 41 + − 21 41 + − 5 7 = − 5 7

b) 1 28 + − 1 14 + 3 28 + − 1 7 + 3 14 = 1 28 + 3 28 + − 1 14 + 3 14 + − 1 7 = 1 7

c)  1 2 + − 2 3 + 3 4 + − 4 5 + 5 6 + − 5 6 + 4 5 + − 3 4 + 2 3 + − 1 2 = 1 2 + − 1 2 + 3 4 + − 3 4 + − 4 5 + 4 5 + 5 6 + − 5 6 = 0