làm mỗi bài 7.2.11b thôi
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XI
1, than
2, whole
3, in
4, much
5,on
6, is
7, surface
8, to
9, word
10, mile
is having
has
takes
to stay
drinks
is eating
is
speaks
has been
has visited
is having
has
takes
to stay
drinks
is eating
is
speaks
has been
has visited
Bài 2:
a: \(x^2+6x+9=\left(x+3\right)^2\)
b: \(4x^2+4x+1=\left(2x+1\right)^2\)
c: \(4x^2-12xy+9y^2=\left(2x-3y\right)^2\)
d: \(x^4-4x^2+4=\left(x^2-2\right)^2\)
Bài 3:
a: \(\left(x-2\right)\left(x^2+2x+4\right)-\left(x^3+2\right)\)
\(=x^3-8-x^3-2\)
=-10
b: \(\left(x+4\right)\left(x^2-4x+16\right)-\left(x-4\right)\left(x^2+4x+16\right)\)
\(=x^3+64-x^3+64\)
=128
Bài 6:
a) Vì $D$ là trung điểm $AC$ nên $AD=DC$. Do đó:
\(\frac{S_{ABD}}{S_{BDC}}=\frac{AD}{DC}=1\)
$\Rightarrow S_{ABD}=S_{BDC}$
b) Ta có: $EC<BC\Rightarrow \frac{EC}{BC}<1$
$\frac{S_{AEC}}{S_{ABC}}=\frac{EC}{BC}<1$
$\Rightarrow S_{AEC}<S_{ABC}$
c) Mình nghĩ lớp 5 chưa đủ kiến thức để làm câu này
d) \(xy+5x-7y=35\)
\(\Leftrightarrow\left(xy+5x\right)-\left(7y+35\right)=0\)
\(\Leftrightarrow\left(y+5\right).\left(x-7\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-7=0\\y+5=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=7\\y=-5\end{matrix}\right.\)