中二（公式）

8a^2b/12ab^3c^2
= 4ab(2a)/(4ab * 3b^2c^2)
= 2a/(3b^2c^2)

pq/p^2q-pq^2
= pq/[pq (p - q)]
= 1/(p-q)

y+2/3y+6
= (y+2)/[3(y+2)]
= 1/3

使x成為公式y=mx+c的主項。
y = mx + c
=> y - c = mx + c - c .......... 兩邊各減 c
=> y - c = mx
=> mx = y - c .......... 左右互換
=> mx/m = (y - c)/m .......... 兩邊各除 m
=> x = (y - c)/m

使B成為公式A=2B/B+C的主項。
A = 2B/(B+C)
=> A(B+C) = 2B/(B+C) * (B+C) .......... 兩邊各 * (B+C)
=> A(B+C) = 2B
=> AB + AC = 2B
=> AC = 2B - AB
=> AC = B(2 - A)
=> B = AC/(2 - A)

使a成為公式2n/a+n/b=4的主項。
2n/a + n/b = 4
=> 2n/a = 4 - n/b
=> 2n/a = (4b-n)/b
=> 2n/a * ab = (4b-n)/b * ab .......... 兩邊各*ab
=> 2bn = (4b-n)a
=> a(4b-n) = 2bn
=> a = 2bn/(4b-n)

使y成為公式6a/x-2a/y=1的主項。
6a/x - 2a/y = 1
=> 6a/x - 1 = 2a/y
=> (6a/x - 1) xy = 2a/y * xy .......... 兩邊各*xy
=> 6ay - xy = 2ax
=> 6ay - 2ax = xy
=>2a(3y - x) = xy
=> a = xy/[2(3y-x)]

8a^2b/12ab^3c^2
=2a/3b^2c^2

第2條唔係太明個題目

y+2/3y+6
=1/3

x=(y-c)/m

B=-(AC/A-2)

a=2bn/(4b-n)

y=-2ax/(x-6a)