Sửa đề : `(5a+33b)/(5a-3b) to (5a+3b)/(5a-3b)`
Đặt `a/b=c/d=k`
`to {(a=bk),(c=dk):}`
`=>`
`(5a+3b)/(5a-3b) \ = (5bk+3b)/(5bk-3b)`
`\qquad\qquad\qquad\qquad=(b(5k+3))/(b(5k-3))=(5k+3)/(5k-3) \ \ (2)`
`(5c+3d)/(5c-3d) \ = (5dk+3d)/(5dk-3d)`
`\qquad\qquad\qquad\qquad=(d(5k+3))/(d(5k-3))=(5k+3)/(5k-3) \ \ (2)`
Từ `(1)` và `(2) to (5a+3b)/(5a-3b)=(5c+3d)/(5c-3d)`