\(a,27.5^2-25.127=27.25-25.127=25\left(27-127\right)=25.\left(-100\right)=-2500\\ b,\dfrac{-5}{12}+\dfrac{3}{4}+\dfrac{1}{-3}=\dfrac{-5}{12}+\dfrac{9}{12}-\dfrac{4}{12}=\dfrac{0}{12}=0\)

a = -2500

b = 0

a, \(A=2\sqrt{3}-\sqrt{12}-\sqrt{9}\)

\(=2\sqrt{3}-2\sqrt{3}-3=-3\)

b, \(B=\sqrt{3}\left(\sqrt{12}+\sqrt{27}\right)\)

\(=\sqrt{3}\left(2\sqrt{3}+3\sqrt{3}\right)\)

\(=\sqrt{3}.5\sqrt{3}=5.3=15\)

\(a,=\dfrac{21}{48}+\dfrac{10}{48}=\dfrac{31}{48}\\ b,=\dfrac{44}{60}-\dfrac{25}{60}=\dfrac{19}{60}\)

a) 1-3+5-7+9-12+15-18

= (1+ 9) - (3+7) + (5+15) - (12+18) 

= 10 - 10 + 20 - 30 = -10.

b) (-2)+5-7+9-11+13-15+19-21

= 5 - 11 - 2 -2 = 5 - (11+2+2)

= 5 - 15 = -10 

Bài 1: 

a) Ta có: 1-3+5-7+9-12+15-18

=(1+9)-(3+7)+(5+15)-(12+18)

=10-10+20-30

=-10

b) Ta có: \(\left(-2\right)+5-7+9-11+13-15+19-21\)

\(=3+2+2+4-21\)

\(=5+6-21\)

=11-21=-10

Bài 5) Tính giá trị của biểu thức

a) A=1.2+2.3+3.4+...+9.10

b) B=3.4+4.5+5.6+...+198.199+199.200

c) C=1.2.3+2.3.4+3.4.5+...+8.9.10

d) D=31.32.33+32.33.34+...+58.59.60

e) E=1.3+3.5+5.7+...+95.97+97.99

f) F=51.53+53.55+...+153.155+155.157

g) G=1.3.5+3.5.7+...+15.17.19+17.19.21

h) H=2.4+4.6+6.8+...+96.98+98.100

b: =-45-27+8=-72+8=-64

c: =12:6=2

d: =-24:8=-3

e: =-36:9=-4

f: =14:7=2

a)

\(-12:\left(\dfrac{3}{4}-\dfrac{5}{6}\right)^2\)

\(=-12:\left(\dfrac{18}{24}-\dfrac{20}{24}\right)^2\)

\(=-12:\left(\dfrac{-1}{12}\right)^2\)

\(=-12:\dfrac{1}{144}\)

\(=-12\times\dfrac{144}{1}\)

\(=-1728\)

b)

\(\left(2^2:\dfrac{4}{3}-\dfrac{1}{2}\right)\times\dfrac{6}{5}-17\)

\(=\left(4\times\dfrac{3}{4}-\dfrac{1}{2}\right)\times\dfrac{6}{5}-17\)

\(=\left(3-\dfrac{1}{2}\right)\times\dfrac{6}{5}-17\)

\(=\dfrac{5}{2}\times\dfrac{6}{5}-17\)

\(=3-17\)

\(=-14\)

a)\(=-12:\left(-\dfrac{1}{12}\right)^2\)
\(=-12:\dfrac{1}{144}\)\(=-12.144=-1728\)
b)\(=\left(8:\dfrac{4}{3}-\dfrac{1}{2}\right).\dfrac{6}{5}-17\)
\(=\left(6-\dfrac{1}{2}\right).\dfrac{6}{5}-17\)
\(=\dfrac{11}{2}.\dfrac{6}{5}-17=\dfrac{33}{5}-17=\dfrac{33}{5}-\dfrac{85}{5}=-\dfrac{2}{5}\)

   

a) (3a + 1)³ = (3a)³ + 3.(3a)².1 + 3.3a.1² + 1³

                   = 27a³ + 27a² + 9a + 1

b) (4 - 2b)³ = 4³ - 3.4².2b + 3.4.(2b)² - (2b)³

                   = 64 - 96b + 48b² - 8b³

c: Ta có: \(C=\sqrt{3-\sqrt{5}}+\sqrt{3+\sqrt{5}}\)

\(=\dfrac{\sqrt{6-2\sqrt{5}}+\sqrt{6+2\sqrt{5}}}{\sqrt{2}}\)

\(=\dfrac{\sqrt{5}-1+\sqrt{5}+1}{\sqrt{2}}=\sqrt{10}\)

`a, = 53 xx (12+172 -84)`

`= 53 xx 100`

`=5300`

`b,= 2018 xx (91-45-46)`

`= 2018 xx 0`

`=0`