PHÂN TÍCH:
a) \(\left(x+2\right)\left(x-4\right)\left(x+6\right)\left(x-12\right)+36x^2\)
b) \(4\left(x+5\right)\left(x+6\right)\left(x+10\right)\left(x+12\right)-3x^2\)
c) \(\left(x-18\right)\left(x-7\right)\left(x+35\right)\left(x+90\right)-67x^2\)