先化简,再求值：2(m+4n)^2-(m-n)^2-(m-2n)(m-8n),其中m=-1/14,n=2
问题描述：
先化简,再求值：2(m+4n)^2-(m-n)^2-(m-2n)(m-8n),其中m=-1/14,n=2
答
2(m+4n)^2-(m-n)^2-(m-2n)(m-8n)
=2m^2+16mn+32n^2-m^2+2mn-n^2-m^2+10mn-16n^2
=28mn+15n^2
=28*(-1/14)*2+15*2^2
=-4+60
=56