1. a^2-8ab+16b^2-8ab-17b= a^2-16ab+16b^2-17b
2. -9c^2+9c^2+6cd+d^2-d^2= 6cd
3. (5a-6)×(5a-6-(5a+6))= (5a-6)×(5a-6-5a-6)= (5a-6)×(-12)= -12 (5a-6)
4. (7b-t)×(t+7b)+(t7b)^2= (t+7b)×(7b-t+t+7b)= (t+7b)×14b= 14b×(t-7b)
5. 18b+27-16b^2-24b+16b^2+8b+1= 2b+28