Factorize the following :
28a2+14a2b2−21a4
HCF of 28, 14, 21 = 7
HCF of a2,a2,a4=a2
HCF of 1,b2,1=1
∴ 28a2+14a2b2−21a4=7a2
(4+2b2−3a2)