\(a,21-22+23-24=-1+\left(-1\right)=-2\\ b,125-\left(115-99\right)=125-115+99=10+99=109\)

a) 21 - 22 + 23 - 24

= (21 + 23) + (-22 - 24)

= 44 - 46

= -2

b) 125 - (115 - 99)

= 125 - 115 + 99

= 10 + 99

= 109

a, - 2

b, 109

a) 21 - 22 + 23 - 24

= (21 - 22) + (23 - 24)

= (-1) + (-1)  = -2

b) 125 - (115 - 99)

= 125 - 115 + 99

= (125 - 115) + 99

 = 10 + 99 = 109.

\(a.21-22+23-24\)

\(=\left(-1\right)+\left(-1\right)=-2\)

\(b.125-\left(115-99\right)\)

\(=125-16=109\)

21-22+23-24

= (-1)+(-1)

=-2

125-(115-99)

= 125-16

=109

a) 21-22+23-24

=-1+(-1)

=-2

b) 125-(115-99)

=125-115+99

=10+99

=109

Bài 3.21:

b: =28+19-28-32+57

=76-32

=44

\(a)3784+23-3785-15\)

\(= \left(3784-3785\right)+\left(23-15\right)\)

\(=-1+8=7\)

\(b)21+22+23+24-11-12-13-14\)

\(=\left(21-11\right)+\left(22-12\right)+\left(23-13\right)+\left(24-14\right)\)

\(=10+10+10+10=40\)

a)3784+23-3785-15=(3784-3785)+(23-15)=(-1)+8=7

b)21+22+23+24-11-12-13-14=(21-11)+(22-12)+(23-13)+(24-14)

=10+10+10+10=4X10=40

Học tốt

Câu 5:

a: \(31\cdot\left(-18\right)+31\cdot\left(-81\right)-31\)

\(=31\left(-18-81-1\right)\)

\(=31\cdot\left(-100\right)=-3100\)

b: \(\left(-12\right)\cdot47+\left(-12\right)\cdot52+\left(-12\right)\)

\(=\left(-12\right)\left(47+52+1\right)\)

\(=-12\cdot100=-1200\)

c: \(13\cdot\left(23+22\right)-3\cdot\left(17+28\right)\)

\(=13\cdot45-3\cdot45\)

\(=45\cdot10=450\)

d: \(-48+48\left(-78\right)+48\left(-21\right)\)

\(=48\left(-1-78-21\right)\)

\(=48\left(-100\right)=-4800\)

Câu 4:

a: \(\left(-6-2\right)\left(-6+2\right)=\left(-8\right)\cdot\left(-4\right)=32\)

b: \(\dfrac{\left(7\cdot3-3\right)}{-6}=\dfrac{21-3}{-6}=\dfrac{18}{-6}=-3\)

c: \(\left(-5+9\right)\cdot\left(-4\right)=4\cdot\left(-4\right)=-16\)

d: \(\dfrac{72}{-6\cdot2+4}=\dfrac{72}{-12+4}=\dfrac{72}{-8}=-9\)

1−2−3+4+5−6−7+8+...+21−22−23+24+25

= (1 - 2 - 3 + 4) + (5 - 6 - 7 + 8) + ... + (21 - 22 - 23 + 24) + 25=(1−2−3+4)+(5−6−7+8)+...+(21−22−23+24)+25

= 0 + 0 + ... + 0 + 25=0+0+...+0+25

= 25

a)21-22+23-24

(22-21)+(24-23)

1+1=2

b)125-(115-99)

125-16

=109

a = -1

b =11 nhớ k

a) 21-22+23-24
=(21-22)+(23-24)
=(-1)+(-1)
=-2
b)125-(115-99)
=125-115+99
=(125-115)+99
=10+99
=109

\(\text{a.61 x 23 + 39 x 22}\)

\(=61.22+1+39.22\)

\(=22.\left(61+39\right)+1\)

\(=22.100+1\)

\(=2200+1\)

\(=2201\)

mình chỉ làm được 1 câu thôi

hok tốt

61*23+39*22

=(61+39)*22+61

=100*22+61

=2200+61

=2261

61 x 23 + 39 x 22 = 61 x ( 22 + 1 ) + 39 x 22 = 61 x 22 + 61 + 39 x 22 = 22 x ( 61 + 39 ) + 61 = 22 x 100 + 61 = 2 200 +61 = 2 261