= 72 x ( 2 + 3 + 5 )

= 72 x 10 

= 720

khoảng cách là:

7,22-5,72=1,5

có số số hạng là:

(34,22-5,72):1,5+1=20(số)

tổng là:

(34,22+5,72)x20:2=399,4

đáp số 399,4 nha bạn

27,89   nha

27,89 

-HT-

27,89 nha bạn

a) \(21^{15}=21^{3.5}=\left(21^3\right)^5=9261^5\)

Vì \(9261>27\Rightarrow9261^5>27^5\Rightarrow21^{15}>27^5\)

b) \(15^{12}=\left(3.5\right)^{12}=3^{12}.5^{12}\)

\(81^3.125^5=\left(3^4\right)^3.\left(5^3\right)^5=3^{4.3}.5^{3.5}=3^{12}.5^{15}\)

Vì \(3^{12}=3^{12}\)mà \(5^{12}< 5^{15}\Rightarrow3^{12}.5^{12}< 3^{12}.5^{15}\Rightarrow15^{12}< 81^3.125^5\)

72 x 2 +72 x 3+ 72 x 5

=72 x (2+3+5)

=72 x 10

=720

72 x 2 +  72 x 3 + 72 x 5 = 72x(2+3+5)

                                   =72x10

                                   =720

c) \(\left|x\right|=3,5\Rightarrow\left[{}\begin{matrix}x=3,5\\x=-3,5\end{matrix}\right.\)

d) \(\left|x\right|=-2,7\Rightarrow x\in\varnothing\) 

l) \(\left|x+\dfrac{3}{4}\right|-5=-2\Rightarrow\left|x+\dfrac{3}{4}\right|=3\)

\(\Rightarrow\left[{}\begin{matrix}x+\dfrac{3}{4}=3\\x+\dfrac{3}{4}=-3\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=3-\dfrac{3}{4}\\x=-3-\dfrac{3}{4}\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=\dfrac{9}{4}\\x=\dfrac{15}{4}\end{matrix}\right.\)

Đính chính câu l \(x=-\dfrac{15}{4}\) không phải \(x=\dfrac{15}{4}\)

c) x = 3,5 hoặc -3,5

d) x = -2,7

e) x = -1,27

f) x = 0

g) x = -2

h) x = 0

l) x = 9/4

   x = -15/4

\(2^{500}\)và  \(5^{200}\)

\(2^{500}=\left(2^5\right)^{100}=32^{100}\)

\(5^{200}=\left(5^2\right)^{100}=25^{100}\)

Ta thấy :

 \(32^{100}>25^{100}\Rightarrow2^{500}>5^{200}\)

\(31^{11}\) và  \(17^{14}\)

\(31^{11}< 32^{12}=\left(2^5\right)^{12}\)

\(17^{14}< 18^{14}=\left(9.2\right)^{14}\)

Ta thấy \(\left(2^5\right)^{12}< \left(9.2\right)^{14}\Rightarrow31^{11}>17^{14}\)

\(5^{23}\)=     \(5\cdot5^{22}\)<     \(6\cdot5^{22}\)

5²³ < 6.5²²

72⁴⁵ - 72⁴⁴ > 72⁴⁴ - 72⁴³

Giải:

5²³ < 6. 5²²

72⁴⁵-72^{44 =} 72⁴⁴ -72⁴³

a) `1/2 xx 5/4 + 1/2 xx 3/4 + 1/2`

`=1/2 xx (5/4 + 3/4 + 1)`

`=1/2 xx 3`

`=3/2`

b) `72/95 xx 64/72 xx 95/72 xx 14/86 xx 72/64 xx 86/14`

`=(72xx64xx95xx14xx72xx86)/(95xx72xx72xx86xx64xx14)`

`= 1`.

a)1/2.(5/4+3/4+1)

=1/2.3

=3/2

b)=(72/95.95/72).(64/72.72/64).(14/86.86/14)

=1.1.1=1

72×35−72×5=72×(35−5)=72×30=2160

Vậy 72×35−72×5=2160

Đáp án D