markdown左对齐
在需要左对齐的部分前后加上一些东西，每行最前面加上&即可。
若要等式对齐，则将&放在等号前面。要按哪个字符对齐，就将&放在哪个字符后面。
$$
begin{aligned}
& a=1\
& a+b=2\
& a+b+c=3
end{aligned}
$$
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begin{aligned} & a=1\ & a+b=2\ & a+b+c=3 end{aligned}
a=1a+b=2a+b+c=3
等式对齐
$$
begin{aligned}
x^2 + 6x + 8 &= (x+3)^2-9+8 \
&= (x+3)^2-1 \
&= (x+4)(x+2)
end{aligned}
$$
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begin{aligned} (x+1)^2 &= (x+1)cdot (x+1) \ &= x(x+1)+(x+1) \ &= x^2+x+x+1 \ &= x^2+2x+1 end{aligned}
(x+1)2=(x+1)⋅(x+1)=x(x+1)+(x+1)=x2+x+x+1=x2+2x+1
按某个字符对齐
$$
begin{aligned}
I &like running.\
He &like swimming.\
She &like dancing.
end{aligned}
$$
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begin{aligned} I &like running.\ He &like swimming.\ She &like dancing. end{aligned}
I He She like running.like swimming.like dancing.