x^2+x+1/4
=(x+1/2)^2
8(a+2b)方-18(2a-b)方
=8a^2+32ab+32b^2-72a^2+72ab-18b^2
=-64a^2+14b^2+104ab
=-2(32a^2-52ab-7b^2)
=-2(4a-7b)(8a+b)