6.4^2-3.6^2;
=(6.4+3.6)(6.4-3.6)
=10×2.8
=28
2012^2-2010×2014;
=2012²-(2012-2)(2012+2)
=2012²-2012²+4
=4
800^2-1600×798+798^2;
=(800-798)²
=2²
=4
1.4^2×9-2.3^2×36
=(1.4×3)²-(2.3×6)²
=4.2²-13.8²
=(4.2+13.8)(4.2-13.8)
=18×(-9.6)
=-172.8