数学题(用十字相乘法)
4n^2+4n-15
6a^2+a-35
5x^2-8x-13
4x^2+15x+9
15x^2+x-2
6y^2+19y+10
20-9y-20y^2
7(x-1)^2+4(x-1)(x+2)-20(y+2)^2