how to factorize?

4-20(c-3d)+25(c-3d)^2

= (2)^2 - 2(2)(5)(c-3d) +[5(c-3d)]^2

=[4-5(c-3d)]^2

=(15d-5c+4)^2//

2008-02-12 19:45:39 補充：
=(15d-5c+2)^2//

2008-02-12 19:46:06 補充：
=[2-5(c-3d)]^2=(15d-5c+2)^2//

4 - 20(c-3d) + 25(c-3d)^2
= 2^2 + 2(2)(5)(c - 3d) + (5(c - 3d))^2
=(2 + 5(c - 3d))^2
=(2 + 5c - 15d)^2