Câu 1: 

                         [(4x+28).3+5.5]:5=35

                         [(4x+28).3+5.5]=35.5 

                         (4x+28).3+25=175 

                          (4x+28).3=175-25

                          (4x+28).3=150 

                         4x+28=150:3 

                          4x+28=50 

                           4x=50-28 

                             4x=22 

                            x=22:4 

                            x=5,5

a.\([\)(4x+28).3+5.5\(]\):5=35\(\Leftrightarrow\)4(x+7).3+25=175\(\Leftrightarrow\)4(x+7).3=150\(\Leftrightarrow\)4.(x+7)=50\(\Leftrightarrow\)x+7=\(\frac{25}{2}\)\(\Leftrightarrow\)x=\(\frac{11}{2}\)

b.720:\([\)41-(2x-5)\(]\)=40\(\Leftrightarrow\)41-(2x-5)=18\(\Leftrightarrow\)2x-5=23\(\Leftrightarrow\)x=14

c.3x+8x-30=25\(\Leftrightarrow\)11x=55\(\Leftrightarrow\)x=5

a) [( 4x + 28 ) . 3 + 5.5 ] : 5 = 35

\(\Leftrightarrow\)[( 4x + 28 ) . 3 + 25 ] = 35.5 = 175

\(\Rightarrow\left(4x+28\right).3=175-25=150\)

\(\Rightarrow4x+28=150:3=50\)

\(\Rightarrow4x=50-28=22\)

\(\Rightarrow x=\frac{22}{4}=\frac{11}{2}=5,5\)

b) 720 : [ 41 - ( 2 . x - 5 )] = 40

\(\Rightarrow41-\left(2x-5\right)=720:40=18\)

\(\Rightarrow2x-5=41-18=23\)

\(\Rightarrow2x=23+5=28\)

\(\Rightarrow x=28:2=14\)

c) 3 . x + 8 . x - 30 = 25

\(\Rightarrow x\left(3+8\right)-30=25\)

\(\Rightarrow11x=25+30=55\)

\(\Rightarrow x=55:11=5\)

dễ mà k nhé

=3.4.5/4.5.6

=3/6=1/2

Ta có:

\(\frac{3}{4}\cdot\frac{4}{5}\cdot\frac{5}{6}=\frac{3\cdot4\cdot5}{4\cdot5\cdot6}=\frac{3}{6}=\frac{1}{2}\)

=1/2 nha bạn

AI CÓ LÒNG NÂN TỪ THÌ TK CHO MK NHA MK ĐANG ÂM ĐIỂM NÈ HU HU

vào luôn đi

đợi tui làm nốt bài đã

\(\frac{\left(-5\right)^{60}.30^5}{15^5.5^{61}}\)

\(=\frac{\left(-5\right)^{60}.\left(5.3.2\right)^5}{\left(3.5\right)^5.5^{61}}\)

\(=\frac{\left(-5\right)^{60}.5^5.3^5.2^5}{3^5.5^5.5^{61}}\)

\(=-5.2^5=-160\)

\(1.1!+2.2!+3.3!+4.4!+5.5!\)  

= \(\left(2-1\right).1!+\left(3-1\right).2!+\left(4-1\right).3!+\left(5-1\right).4!+\left(6-1\right).5!\) 

= \(2!-1!+3!-2!+4!-3!+5!-4!+6!-5!\) 

= \(6!-1!\) = \(720-1=719\)

Đề còn thiếu 1 điều kiện nữa là \(n>0\)

Đặt \(A=\frac{4}{5.2!}+\frac{4}{5.3!}+\frac{4}{5.4!}+...+\frac{4}{5.n!}\) ta có : 

\(A=\frac{4}{5}\left(\frac{1}{2!}+\frac{1}{3!}+\frac{1}{4!}+...+\frac{1}{n!}\right)\)

Để \(A< 0,8\) thì \(\frac{1}{2!}+\frac{1}{3!}+\frac{1}{4!}+...+\frac{1}{n!}< 1\)

Đặt \(B=\frac{1}{2!}+\frac{1}{3!}+\frac{1}{4!}+...+\frac{1}{n!}\) ta có : 

\(B< \frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{\left(n-1\right)n}\)

\(B< \frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{n-1}+\frac{1}{n}\)

\(B< 1-\frac{1}{n}< 1\)

\(\Rightarrow\)\(B< 1\) ( đpcm ) 

Suy ra : \(A=\frac{4}{5}.B=0,8.B< 0,8\) ( vì \(B< 1\) ) 

Vậy \(\frac{4}{5.2!}+\frac{4}{5.3!}+\frac{4}{5.4!}+...+\frac{4}{5.n!}< 0,8\)

Chúc bạn học tốt ~ 

50

5.5+5.5=25+25=50

ok 50

= 625

5.5:5.5=25:25=1

1

minh chon B k di

BT B k minh nha nhanh nhat do

Ket qua la bt C 

\(a)\frac{(-5)^{60}.30^5}{15^5.5^{61}}=\frac{(5.2.3)^5}{(5.3)^5.5}=\frac{5^5.2^5.3^5}{5^5.3^5.5} =\frac{2^5}{5}=\frac{32}{5}\)

\(b) \frac{(-3)^{10}.15^5}{25^3.(-9)^7}=\frac{(-3)^{10} .(3.5)^5}{(5^2)^3.[(-3).3]^7}=\frac{(-3)^{10}.3^5.5^5}{5^6.(-3)^7.3^7}=\frac{(-3)^3}{5.3^2}=\frac{-3}{5}\)

~ Hok tốt a~