C2 :

\(2\cdot3^{x+2}+4\cdot3^{x+1}=10\cdot3^{2019}\)

\(2\cdot3\cdot3^{x+1}+4\cdot3^{x+1}=10\cdot3^{2019}\)

\(6\cdot3^{x+1}+4\cdot3^{x+1}=10\cdot3^{2019}\)

\(\left(6+4\right)\cdot3^{x+1}=10\cdot3^{2019}\)

\(10\cdot3^{x+1}=10\cdot3^{2019}\)

\(\Rightarrow x+1=2019\)

\(x=2019-1\)

\(x=2018\)

Vậy x = 2018

Chắc sai =))

\(\frac{1313}{1212}:x=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5}\)

\(\frac{1313}{1212}:x=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}\)

\(\frac{1313}{1212}:x=\frac{1}{1}-\frac{1}{5}+\frac{1}{5}\)

\(\frac{1313}{1212}:x=\frac{4}{5}+\frac{1}{5}\)

\(\frac{1313}{1212}:x=1\)

\(x=\frac{1313}{1212}:1\)

\(x=\frac{13}{12}\)

Lời giải 

\(\frac{1313}{1212}:x=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}\)

\(\frac{1313}{1212}:x=\frac{1}{1}-\frac{1}{5}+\frac{1}{5}\)

\(\frac{1313}{1212}:x=\frac{4}{5}+\frac{1}{5}\)

\(x=\frac{1313}{1212}:1\)

\(x=\frac{13}{12}\)

số số hạng = (x-1):2 +1 = (x+1)/2
Vài giây trước

2) 1+ 4+ 7+ 10+...+x= 330

tổng = (x+1) . (x+1)/2 : 2 = 25

=> (X+1)^2 = 100

=> x = 9

nhầm 

1) số số hạng = (x-1):2 +1 = (x+1)/2

tổng = (x+1) . (x+1)/2 : 2 = 25

=> (X+1)^2 = 100

=> x = 9

49 - 3 . ( x + 6 ) = 13

3 . ( x + 6 ) = 49 - 13

3 . ( x + 6 ) = 36

x + 6 = 36 : 3

x + 6 = 12

      x = 12 - 6

      x = 6

49 - 3.( x + 6 ) = 13

   3.( x + 6 ) = 36

     x + 6 = 12

    x = 6

Vậy x = 6

#)Giải :

\(9^8:\left(27^3.81^2\right)=\left(3^2\right)^8:\left[\left(3^3\right)^3.\left(3^4\right)^2\right]=3^{16}:\left[3^9.3^8\right]\)

Đến đây ez rùi ^^

9⁸:(27³.81²) = 9⁸:(3^3x3.3^4x2)=9⁸:3¹⁷= \(\frac{1}{3^9}\)

\(9^8:\left(27^3.81^2\right)=3^{16}:\left(3^9.3^8\right)=3^{16}:\left(3^{9+8}\right)=3^{16}:3^{17}=3^{-1}=\frac{1}{3}\)

\(9^8:\left(27^3.81^2\right)\)

\(=3^{16}:\left(3^9.3^8\right)\)

\(=3^{16}:3^{17}\)

\(=\frac{1}{3}\)

???!!!

Ta có 5²⁰¹⁴ - 5²⁰¹³ + 5²⁰¹²

    = 5²⁰¹².(5² - 5 + 1)

    = 5²⁰¹².21

    = 5²⁰¹¹.5.21

    = 5²⁰¹¹.105 \(⋮\)105

=>  5²⁰¹⁴ - 5²⁰¹³ + 5²⁰¹² \(⋮\)105

Ta có :

5²⁰¹⁴ - 5²⁰¹³ + 5²⁰¹² 

= 5²⁰¹² . (5² - 5¹ + 1)

= 5²⁰¹² . (25 - 5 + 1)

= 5²⁰¹² . 21

= 5²⁰¹¹ . 5 . 21

= 5²⁰¹¹ . 105\(⋮\)105

=> 5²⁰¹⁴ - 5²⁰¹³ + 5^{2012 \(⋮\)}105 (đpcm)

~Study well~

#Zu