\(12^8.9^{12}=3^8.\left(2^2\right)^8.9^{12}=9^4.2^{16}.9^{12}=2^{16}.9^{16}=\left(2.9\right)^{16}=18^{16}\)

nên bạn ghi thiếu đề nha, 18¹⁶ mới đúng

\(12^8\)x\(9^{12}=\left(2^3\times3\right)^8\times\left(3^2\right)^{12}\)

\(=2^{16}\times3^8\)

\(=2^{16}\times3^{32}\)

\(=2^{16}\left(3^2\right)^{16}\)

\(=2^{16}\times9^{16}=\left(2\times9\right)^{16}\)

\(=18^{16}\Rightarrow12^8\times9^{12}=18^{16}\)

bạn thử dựa vào mà làm, nó hơi khác vs bài của bn. đây là bài cô giao cho mk thấy tương ự nên mk đăng

12⁸.9¹²=(2².3)⁸.(3²)¹²=2¹⁶.3⁸.3²⁴=2¹⁶.3³²=2¹⁶.(3²)¹⁶=2¹⁶.9¹⁶=(2.9)¹⁶=18¹⁶

=>12⁸.9¹²=18¹⁶

a)8/5-18/27=216/135-90/135=126/135

b)3/5-1/3=9/15-5/15=4/15(rút gọn p/s)

c)1/3-1/5=5/15-3/15=2/15

d)6/7-12/27=162/189-84/189=78/189

a) 8/5 - 18/27

= 8/5 - 2/3

= 24/15 - 10/15

= 14/15

b) 12/20 - 6/18

= 3/5 - 1/3

= 9/15 - 5/15

= 4/15

c) 8/24 - 5/25

= 1/3 - 1/5

= 5/15 - 3/15

= 2/15

d) 18/21 - 12/27

= 6/7 - 4/9

= 54/63 - 28/63

= 26/63

\(12^8.9^{12}=\left(2^2.3\right)^8.\left(3^2\right)^{12}=2^{16}.3^8.3^{24}=2^{16}.3^{32}=2^{16}.\left(3^2\right)^{16}=2^{16}.9^{16}=18^{16}\)

\(12^8.9^{12}=4^8.3^8.9^{12}=2^{16}.9^4.9^{12}=2^{16}.9^{16}=\left(2.9\right)^{16}=18^{16}\left(đpcm\right)\)

\(12^8.9^{12}=(3.2^2)^8.(3^2)^{12}\)

\(=3^8.2^{16}.3^{24}=2^{16}.3^{8+24}=2^{16}.3^{32}\)

\(=2^{16}.9^{16}=(2.9)^{16}=18^{16}\)

Chứng minh : 

12^8 . 9^12 = 18^16 

Biến đổi VT ( vế trái ) : 12^8 . 9^12 = ( 2^2 . 3 )^8 . ( 3^2 )^12

                                                             = 2^16 .3^8 . 3^24 = 2^16 . 3^32 

Biến đổi VP ( vế phải )  : 18^16 = ( 2 . 3^2 )^16 = 2^16 . 3^32 

Vậy VT = VP   

Ta có:+, 12^8. 9^12 = (12^2)^4. (3^3)^4

                             =144^4. 27^4       

                             = 3888^4

           +, 18^16 = (18^4)^4

                         = 104976^4

           Vì 3888^4 < 104976^4 nên 12^8. 9^12< 18^16

                                Vậy 12^8 . 9^12 < 18^16

\(a.\)

\(-\dfrac{2}{9}+\dfrac{7}{-9}=\dfrac{-2}{9}-\dfrac{7}{9}=\dfrac{-2-7}{9}=\dfrac{-9}{9}=-1\)

\(b.\)

\(\dfrac{1}{-6}+\dfrac{13}{-15}=-\dfrac{1}{6}-\dfrac{13}{15}=\dfrac{\left(-1\right)\cdot5-13\cdot2}{30}=\dfrac{-5-26}{30}=\dfrac{-31}{30}\)

\(c.\)

\(\dfrac{5}{-6}+\dfrac{-5}{12}+\dfrac{7}{18}=\dfrac{-5}{6}-\dfrac{5}{12}+\dfrac{7}{18}=\dfrac{\left(-5\right)\cdot6-5\cdot3+7\cdot2}{36}=\dfrac{-31}{36}\)

a) \(\dfrac{-2}{9}+\dfrac{7}{-9}=\dfrac{-2+-7}{9}=-1\) 

b)\(\dfrac{1}{-6}+\dfrac{13}{-15}=\dfrac{-5}{30}+\dfrac{26}{30}=\dfrac{-5+26}{30}=\dfrac{7}{10}\) 

c) \(\dfrac{5}{-6}+\dfrac{-5}{12}+\dfrac{7}{18}=\dfrac{-30}{36}+\dfrac{-15}{36}+\dfrac{18}{36}=\dfrac{-30+-15+18}{36}=\dfrac{-3}{4}\)