in chapter 47,the author or the artist maybe made a small mathematical error in this one,that is (a-b)^2 = a^2-2ab+b^2 not (a-b)^2 = a^2-2ab-b^2
in chapter 47,the author or the artist maybe made a small mathematical error in this one,that is (a-b)^2 = a^2-2ab+b^2 not (a-b)^2 = a^2-2ab-b^2