Xin hay nhất nhé tus ^_^
Bài `3:`
`a)` `(44.52.60):(11.13.15)`
`=` `(44:11).(52:13).(60:15)`
`=` `4.4.4`
`=` `64`
`b)` `(98.7676-9898.76):(2001.2002.2003....2010)`
`=` `(98.76.101-98.101.76):(2001.2002.2003.....2010)`
`=` `0:(2001.2002.2003....2010)`
`=` `0`
`c)` `99-97+95-93+91-89+...+7-5+3-1`
`=` `(99-97)+(95-93)+...+(7-5)+(3-1)`
`=` `2+2+...+2+2`
`=` `2.25`
`=` `50`
`d)` `100+98+96+...+2-97-95-...-1`
`=` `(100+98+96+...+2)-(97+95+...+1)`
`=[(100+2)+(98+4)+...+(52+50)]-[(97+1)+(95+3)+...+(51+47)+49]`
`=` `[102+102+...+102]-[98+98+...+98+49]`
`=` `[102.25]-[98.24+49]`
`=` `2550-[2352+49]`
`=` `2550-2401`
`=` `149`
Bài `4:`
`a)` `(x-42)-110=0`
`x-42=0+110`
`x-42=110`
`x=110+42`
`x=152`
Vậy `x=152`
`b)` `315+(146-x)=401`
`146-x=401-315`
`146-x=86`
`x=146-86`
`x=60`
Vậy `x=60`
`c)` `2436:x=12`
`x=2436:12`
`x=203`
Vậy `x=203`
`d)` `6x-5=613`
`6x=613+5`
`6x=618`
`x=618:6`
`x=103`
Vậy `x=103`
`e)` `74.(x-3)=0`
`x-3=0:74`
`x-3=0`
`x=0+3`
`x=3`
Vậy `x=3`
`f)` `(x-32):16=48`
`x-32=48.16`
`x-32=768`
`x=768+32`
`x=800`
Vậy `x=800`
`f)` `814-(x-305)=712`
`x-305=814-712`
`x-305=102`
`x=102+305`
`x=407`
Vậy `x=407`
`g)` `6x+4x=2010`
`(6+4)x=2010`
`10x=2010`
`x=2010:10`
`x=201`
Vậy `x=201`
`h)` `(x-4)(x-7)=0`
`⇒` \(\left[ \begin{array}{l}x-4=0\\x-7=0\end{array} \right.\)
`⇒` \(\left[ \begin{array}{l}x=4\\x=7\end{array} \right.\)
Vậy `x∈{4;7}`
`i)` `xy-2x=5`
`x(y-2)=5`
`⇒` $\begin{cases} x∈Ư(5)\\y-2∈Ư(5) \end{cases}$
`⇒` `(x;y-2)∈{±1;±5}`
TH`1:` `x=1`
`⇒` `y-2=5`
`⇒` `y=5+2=7`
TH`2:` `x=-1`
`⇒` `y-2=-5`
`⇒` `y=-5+2=-3`
TH`3:` `x=5`
`⇒` `y-2=1`
`⇒` `y=1+2=3`
TH`4:` `x=-5`
`⇒` `y-2=-1`
`⇒` `y=-1+2=1`
Vậy `(x;y)∈{(1;7),(-1;-3),(5;3),(-5;1)}`
