= 25/49 *( 21/29-7/29) +24/49 * 15/29

=25/49*14/29+ 24/49*15/29

   BẠN TỰ LÀM TIẾP NHA

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\(\frac{25}{49}.\frac{21}{29}-\frac{25}{49}.\frac{7}{29}+\frac{24}{49}.\frac{15}{29}\)

\(=\frac{25}{49}.\left(\frac{21}{29}-\frac{7}{29}\right)+\frac{24}{49}.\frac{15}{29}\)

\(=\frac{25}{49}.\frac{14}{29}+\frac{24}{49}.\frac{15}{29}\)

\(=\left(\frac{25}{49}+\frac{24}{49}\right).\left(\frac{14}{29}+\frac{15}{29}\right)\)

\(=1.1=1\)

a, (18+29) +(158-18-29)

= 18+29+158-18-29

= (18-18) +(29-29)+ 158

= 158

b, (13-135+49)- (13+49)

= 13-135+49-13-49

= (13-13) +(49-49) -135

= 135

a, \(\left(18+29\right)+\left(158-18-29\right)\)

\(=18+29+158-18-29\)

\(=\left(18-18\right)+\left(29-29\right)+158\)

\(=158\)

b,

\(\left(13-135+49\right)-\left(13+49\right)\)

\(=13-135+49-13-49\)

= \(\left(13-13\right)+\left(49-49\right)-135\)

= \(-135\)

\(a,\left(13+49\right)-\left(13-135\right)\)

= \(13+49-13+135\)

= \(13-13+49+135\)

= \(184\)

\(b,\left(18+29\right)+\left(158-18-29\right)\)

= \(18+29+158-18-29\)

= \(158\)

\(c,4.5^2-3.\left(24-9\right)\)

= \(4.25-\left(72-27\right)\)

= \(100.-45\)

= \(55\)

\(d,\left[93-\left(20-7\right)\right]:16\)

= \(\frac{93-20+7}{16}\)

= \(\frac{80}{16}\)

= \(5\)

mình ghi lộn dấu + thành dấu = ở câu a nhé

7)\(\dfrac{-19}{34}\left(\dfrac{17}{19}+\dfrac{49}{18}\right)+\dfrac{49}{18}\left(\dfrac{19}{34}-\dfrac{18}{7}\right)\)

=\(\dfrac{-19}{34}.\dfrac{17}{19}+\dfrac{49}{18}.\dfrac{-19}{34}+\dfrac{49}{18}.\dfrac{19}{34}-\dfrac{18}{7}.\dfrac{49}{18}\)

=\(\dfrac{1}{2}+\left(\dfrac{49}{18}.\dfrac{-19}{34}+\dfrac{49}{18}.\dfrac{19}{34}\right)-7\)

=\(\dfrac{1}{2}+\left[\dfrac{49}{18}\left(\dfrac{-19}{34}+\dfrac{19}{34}\right)\right]-7\)

=\(\dfrac{1}{2}+0-7=\dfrac{-13}{2}\)

8)\(\dfrac{29}{32}\left(\dfrac{41}{36}-\dfrac{32}{58}\right)-\dfrac{41}{36}\left(\dfrac{29}{32}+\dfrac{18}{41}\right)\)

=\(\dfrac{29}{32}.\dfrac{41}{36}-\dfrac{29}{32}.\dfrac{32}{58}-\dfrac{41}{36}.\dfrac{29}{32}+\dfrac{18}{41}.\dfrac{41}{36}\)

=\(\left(\dfrac{29}{32}.\dfrac{41}{36}-\dfrac{41}{36}\dfrac{29}{32}\right)-\dfrac{29}{32}.\dfrac{32}{58}+\dfrac{18}{41}.\dfrac{41}{36}\)

=\(0-\dfrac{1}{2}+\dfrac{1}{2}=0\)

x=20     

Lí do = 0 nè:

\(\frac{x-39}{19}+\frac{x-49}{29}=\frac{x-5}{39}+\frac{x-69}{49}\)

=> \(\frac{x-39}{19}+\frac{x-49}{29}=0+\left(\frac{x-5}{39}+\frac{x-69}{49}\right)\)

=> \(\frac{x-39}{19}+\frac{x-49}{29}-\left(\frac{x-5}{39}+\frac{x-69}{49}\right)=0\)

=> \(\frac{x-39}{19}+\frac{x-49}{29}-\frac{x-5}{39}-\frac{x-69}{49}=0\)

\(\frac{-29}{73}>\frac{-80}{49}\)

Giải chi tiết hộ vs

\(\frac{x-39}{19}+\frac{x-49}{29}=\frac{x-59}{39}+\frac{x-69}{49}\)

Công mỗi vế cho 2 ta được:

\(\frac{x-39}{19}+\frac{x-49}{29}+2=\frac{x-59}{39}+\frac{x-69}{49}+2\)

\(\frac{x-39}{19}+1+\frac{x-49}{29}+1=\frac{x-59}{39}+1+\frac{x-69}{49}+1\)

\(\frac{x-39}{19}+\frac{19}{19}+\frac{x-49}{29}+\frac{29}{29}=\frac{x-59}{39}+\frac{39}{39}+\frac{x-69}{49}+\frac{49}{49}\)

\(\frac{x-20}{19}+\frac{x-20}{29}=\frac{x-20}{39}+\frac{x-20}{49}\)

\(\frac{x-20}{19}+\frac{x-20}{29}-\frac{x-20}{39}-\frac{x-20}{49}=0\)

\(\left(x-20\right).\frac{1}{19}+\left(x-20\right).\frac{1}{29}-\left(x-20\right).\frac{1}{39}-\left(x-20\right).\frac{1}{49}=0\)

Đặt thừa số chung (x-20) ra ngoài

\(\left(x-20\right).\left(\frac{1}{19}+\frac{1}{29}-\frac{1}{39}-\frac{1}{49}\right)=0\)

\(\text{Vì }\frac{1}{19}+\frac{1}{29}-\frac{1}{39}-\frac{1}{49}\ne0\text{ nên }x-20=0\Rightarrow x=20\)

a,x/8=2/x

=>x²=16

=>x=-4;4

vậy x=-4;4

b,\(\frac{x-39}{19}+\frac{x-49}{29}=\frac{x-59}{39}+\frac{x-69}{49}\)

\(\Rightarrow\left(\frac{x-39}{19}+1\right)+\left(\frac{x-49}{29}+1\right)=\left(\frac{x-59}{39}+1\right)+\left(\frac{x-69}{49}+1\right)\)

\(\Rightarrow\frac{x-20}{19}+\frac{x-20}{29}=\frac{x-20}{39}+\frac{x-20}{49}\)

\(\Rightarrow\frac{x-20}{19}+\frac{x-20}{29}-\frac{x-20}{39}-\frac{x-20}{49}=0\)

\(\Rightarrow\left(x-20\right)\left(\frac{1}{19}+\frac{1}{29}-\frac{1}{39}-\frac{1}{49}\right)=0\)

vì \(\frac{1}{19}+\frac{1}{29}-\frac{1}{39}-\frac{1}{49}\ne0\Rightarrow x-20=0\Rightarrow x=20\)

vậy x=20

\(\frac{x}{8}=\frac{2}{x}\Rightarrow x^2=8.2\)

\(x^2=16\Rightarrow x^2=\left(\pm4\right)^2\Rightarrow x=4;x=-4\)

Học tốt

19/41 < 21/41 , 23/53 < 23/49 và 29/61 < 33/65

Suy ra: 19/41 + 23/53 + 29/61 <21/41+ 23/49+ 33/65

Vậy A<B

Ở phép so sánh thứ 3 bạn áp dụng công thức a/b < a+n/b+n với a/b <1 và n là số tự nhiên khác 0.

Chúc bạn học tốt.

Ta có: 

\(\frac{19}{41}< \frac{21}{41}\)

\(\frac{23}{53}< \frac{23}{49}\)

\(\Rightarrow\frac{19}{41}+\frac{23}{53}< \frac{21}{41}+\frac{23}{49}\)

Ta có: \(\hept{\begin{cases}\frac{29}{61}=1-\frac{32}{61}\\\frac{33}{65}=1-\frac{32}{65}\end{cases}}\)

Mà \(\frac{32}{61}>\frac{32}{65}\Rightarrow1-\frac{32}{61}< 1-\frac{32}{65}\Rightarrow\frac{29}{61}< \frac{33}{65}\)

\(\Rightarrow\frac{19}{41}+\frac{23}{53}+\frac{29}{61}< \frac{21}{41}+\frac{23}{49}+\frac{33}{65}\)

\(\Rightarrow A< B\)

Vậy \(A< B\) 

Tham khảo nhé~