Tách ra từng câu rồi đăng thành câu hỏi nhé

Bài 3: 

a: \(x=\dfrac{1}{4}-\dfrac{2}{13}=\dfrac{13}{52}-\dfrac{8}{52}=\dfrac{5}{52}\)

b: \(\dfrac{x}{3}=\dfrac{2}{3}-\dfrac{1}{7}\)

nên \(x\cdot\dfrac{1}{3}=\dfrac{14}{21}-\dfrac{3}{21}=\dfrac{11}{21}\)

hay \(x=\dfrac{11}{21}:\dfrac{1}{3}=\dfrac{11}{7}\)

\(c,\Rightarrow\left|x-\dfrac{1}{9}\right|=-\dfrac{4}{5}\\ \Rightarrow x\in\varnothing\left(\left|x-\dfrac{1}{9}\right|\ge0>-\dfrac{4}{5}\right)\\ d,\Rightarrow\left\{{}\begin{matrix}3x-2=0\\4y-7=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=\dfrac{2}{3}\\y=\dfrac{7}{4}\end{matrix}\right.\\ e,\Rightarrow\left\{{}\begin{matrix}2x+1=0\\x-y=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=-\dfrac{1}{2}\\x=y=-\dfrac{1}{2}\end{matrix}\right.\Rightarrow x=y=-\dfrac{1}{2}\)

\((-12).36 - 12.64 =-432 - 768 =-1200\)

\(21,22+9,072\times10+24,72:12\)

\(=21,22+90,72+2,06\)

\(=111,94+2,06\)

\(=114\)

=21,22+ 90,72+ 2,06

= 111,94 +2,06

= 114

20:

1: Xét ΔACD và ΔABE có

AC=AB

góc A chung

AD=AE

=>ΔACD=ΔABE

2: ΔABE=ΔACD

=>góc ABE=góc ACD

=>góc IBD=góc ICE

3: Xét ΔIBD và ΔICE có

góc IBD=góc ICE
BD=CE
góc IDB=góc IEC
=>ΔIBD=ΔICE

4: ΔIBD=ΔICE

=>IB=IC; ID=IE

=>ΔIBC cân tại I; ΔIDE cân tại I