(3x^2-4x+5)(3x^2+4x-5)
=[3x^2-(4x-5)][3x^2+(4x-5)]
=(3x^2)^2-(4x-5)^2
=9x^4-16x^2+40x-25这样就最简了？怎么还这么长~是啊 都是3项相乘 应该得到9项合并成4项了啊