3/ 4x7 + 1 / 7 x 8 + 5 / 8  x13 + 2 / 13 x 15 + 9 / 15 x 24

= 1/ 4-1/7+ 1 / 7 - 1/8 + 1/ 8 - 1/ 13 + 1/ 13 - 1/ 15 + 1/ 15 - 1/24

= 1/ 4 - 1/24

=5/ 24

\(\frac{3}{4\times7}+\frac{1}{7\times8}+\frac{5}{8\times13}+\frac{2}{13\times15}+\frac{9}{15\times24}\)

=  \(\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+\frac{1}{15}-\frac{1}{24}\)

= \(\frac{1}{4}-\frac{1}{24}\)

=  \(\frac{6}{24}-\frac{1}{24}\)

= \(\frac{5}{24}\)

\(\frac{3}{4.7}+\frac{1}{1.8}+\frac{5}{8.13}+\frac{2}{13.15}+\frac{9}{15.24}\)

Đặt A = ( 3 + 1 + 5 + 2 + 9 ) . \(\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+\frac{1}{15}-\frac{1}{24}\)

      A = 20 . \(\frac{1}{4}-\frac{1}{24}\)

      A = 20 . \(\frac{6}{24}-\frac{1}{24}\)

      A  = 20 . \(\frac{5}{24}\)

      A  = \(\frac{100}{24}\)

Ko chắc

Sai bỏ qua 

Học tốt

# DanLinh

Bạn Dan Linh ơi dãy số: \(\frac{3}{4\times7}+\frac{1}{7\times8}+\frac{5}{8\times13}+\frac{2}{13\times15}+\frac{9}{15\times24}\)

Không có chung ( 3 + 1 + 5 + 2 + 9 ) mà bạn lại đặt ra là sao vậy

  ( 1+2+3+.... +99) x (13x15 -12 x 15- 15)

= ( 1+2+3+.... +99) x 0

=0      

(9999+ 1555144) : 55555 x 0 = 0

               đs : 0

Nhìn vô thấy khúc cuối có biểu thức (13 x 15 - 12 x 15 -15) là dễ rồi!

= 13 x 15 - 12 x 15 - 15 x 1 (Chú ý phần 15 x 1. Vì 15 x 1 cũng bằng 15 nên 15 = 15 x 1)

=15 x (13 - 12 - 1)

=15 x 0

= 0

Đáp số: 0

Quá dễ XD

\(240:\left(5^3-5^3:5^2\right)-3^6:3^4+15\cdot11\cdot\left(13-9\right)\)

\(=240:\left(5^3-5\right)-3^{6-4}+15\cdot11\cdot4\)

\(=240\cdot\left(125-5\right)-3^2+60\cdot11\)

\(=240:120-9+60\cdot\left(10+1\right)\)

\(=2-9+600+60\)

\(=653\)

1.a) 4.(12+88) = 4.100=400

b)7²- 6 .[2.8:8 ]=7²-6.[16:8]=7²-6 .2= 49-12=37  ( tui ko chắc lắm )

2.a) x=26-11=15 

b) (4x-15)³=5³ 

4x-15=5 

4x= 5+15

4x=20

vậy x = 20

Bài 2: 

a: Ta có: x+11=26

nên x=15

b: Ta có: \(\left(4x-15\right)^3=125\)

\(\Leftrightarrow4x-15=5\)

hay x=5

Bài 1: 

\(\Leftrightarrow2^n\cdot\dfrac{9}{2}=9\cdot5^n\)

\(\Leftrightarrow2^n=2\cdot5^n\)

\(\Leftrightarrow2^{n-1}=5^n\)

Bài 2: 

a: \(A=\dfrac{2^8+3^8}{2^8}=1+\dfrac{3^8}{2^8}\)

b: \(B=\left(2^{17}+17^2\right)\cdot\left(9^{15}-15^9\right)\cdot\left(16-16\right)=0\)

\(\dfrac{-2}{9}-\dfrac{3}{4}+\dfrac{3}{5}+\dfrac{1}{15}+\dfrac{1}{57}+\dfrac{1}{3}-\dfrac{1}{36}\)

\(=\left(-\dfrac{2}{9}-\dfrac{3}{4}-\dfrac{1}{36}\right)+\left(\dfrac{3}{5}+\dfrac{1}{15}+\dfrac{1}{3}\right)+\dfrac{1}{57}\)

\(=\dfrac{-8-27-1}{36}+\dfrac{9+1+5}{15}+\dfrac{1}{57}\)

\(=-\dfrac{36}{36}+\dfrac{15}{15}+\dfrac{1}{57}\)

\(=\dfrac{1}{57}\)

giúp mình với

41/16

41/16

15 × (4 - 7) - 15 × (5 - 3)

= 15 × (-3) - 15 × 2

= 15 × (-3 - 2)

= -15 × 5 

= -75

--------

73 × (8 - 59) - 59 × (8 - 73)

= 73 × 8 - 73 × 59 - 59 × 8 + 59 × 73

= 8 × (73 - 59) + 73 × (59 - 59)

= 8 × 14 + 73 × 0

= 8 × 14

= 112

15 x (4-7) - 15 x (5-3)

= 15 x (-3) - 15 x (-2)

= 15 x (-3 - (-2))

= 15 x (-1)

= -15

73 x (8-59) - 59 x (8-73)

= 73 x 8 - 59 x 73 - 59 x (-65)

= 73 x 8 - 59 x (73 - (-65))

= 73 x 8 - 59 x 8

= 8 x (73-59)

= 8 x 14

= 112

a) 15 × (4 - 7) - 15 × (5 - 3)

= 15 × (-3) - 15 × 2

= 15 × (-3 - 2)

= -15 × 5 

= -75

b) 73 × (8 - 59) - 59 × (8 - 73)

= 73 × 8 - 73 × 59 - 59 × 8 + 59 × 73

= 8 × (73 - 59) + 73 × (59 - 59)

= 8 × 14 + 73 × 0

= 8 × 14

= 112