ky−k=y2 Factorize k out ky=k×y −k=−1×k When you factorize, you take the letter(s) common at both sides or the number that divides each numbers out and write the remain(s) in a bracket ky−k=k×y−1×k Bring the k out ⇒k×y−1×k=k(y−1) ky−k=y2 ⇒k(y−1)=y2 Since we are making k the subject (let k stand alone), we divide both sides of the equation by (y−1) so that the (y−1) cancels each other, leaving the k alone. ⇒k=y2∕(y−1)