A)(y+2)ˇ2 - 4yˇ2 = (y+2)ˇ2 - (2y)ˇ2= (y+2+2y)(y+2-2y)=(3y+2)(-y+2)
b)100aˇ2 - (5a+9)ˇ2 = (10a)ˇ2 - (5a+9)ˇ2= (10a+5a+9)(10a-5a-9)=
(15a+9)(5a-9)
c)(t-7)ˇ2 - 9tˇ2=(t-7)ˇ2- (3t)ˇ2 = (t-7+3t)(t-7-3t)=(4t-7)(-2t-7)=-(4t-7)(2t+7)
d)121bˇ2-(7b-3)ˇ2=(11b)ˇ2 - (7b-3)ˇ2 = (11b+7b-3)(11b-7b+3)=(18b-3)(4b+3)= 3.(6b-1)(4b+3)