>>410
(3a-4)^2= (3a-4)(3a-4)=9a^2-12a-12a+16=9a^2-24a+16
(−x−2y)(−x−2y)=x^2+2xy+2xy+4y^2=x^2+4xy+4y^2
(3a−2b)(2b＋3a) =6ab+9a^2-4b^2-6ab=9a^2-4b^2

のはずです