I got this transition. but,can you show what n equations are?

a1 + b1x
=[（b2+c3b3+...+cnbn）a1 +（b2+c3b3+...+cnbn）b1x] /（b2+c3b3+...+cnbn）
= b1[（b2+c3b3+...+cnbn）a1/b1+（b2+c3b3+...+cnbn）x] /（b2+c3b3+...+cnbn）

where - should be corretted to +.

a2+b2x = a2+b2x
a3+b3x = (c3a3+c3b3x)/c3
...
an+bnx = (cnan+cnbnx)/cn

key is factor（b2+c3b3+...+cnbn）.