(x-2)(x+2)+(2x-1)(-2x+1)

(x-2)(x+2)+(2x-1)(-2x+1)
=x^2-4-(2x-1)^2
=x^2-4-4x^2+4x-1
=-3x^2+4x-5

(2x-y)^2=4x^2-4xy+y^2

(3m+2n)^2=9m^2+12mn+4n^2

2（m+4n)^2-(m-n)^2-（m-2n)(m-8n)
=2m^2+16mn+32n^2-m^2+2mn-n^2-m^2+20mn-16n^2
=38mn+15n^2
=38*(-1/14)*2+15*2^2
=458/7

(x-2)(x+2)+(2x-1)(-2x+1)=x^2-4-(4x^2-4x+1)=
-3x^2+4x-5
(2x-y)的2次=4x^2-4xy+y^2
(3m+2n)的2次=9m^2+12mn+4n^2
(m+4n)的2次-(m-n)的2次-（m-2n)(m-8n)
=(m+4n+m-n)(m+4n-m+n)-(m^2-10mn+16n^2)
=10mn+15n^2-m^2+10mn-16n^2
=20mn-m^2-n^2
m=-1/14,n=2
20mn-m^2-n^2=-20/7-1/196-4=-1345/196