Question

factorise 28 c square d square - 21 c square d​

Answer 1

a²-b²+2bc-c²=a² - (b² -2bc +c²)

                   = a² - (b-c)²

                   =(a-(b-c))(a+(b-c))  [using identity a²-b² =(a-b)(a+b)]

                  = (a-b+c)(a+b-c)

hence.,a²-b²+2bc - c²  = (a-b+c)(a+b-c)