kuai，本人急用！！！！过程要有，两道题，第二题可以用全等三角形的知识

显示全部楼层 · 2013-1-24 18:40:28

1.x=n*(n+3) *[(n+1)(n+2)]=(n2+3n)(n2+3n+2)y=(n2+3n+1)(n2+3n+1)设n2+3n=k则x=k(k+2)=k2+2ky=(k+1)2=k2+2k+1显然y>x2.根据内角和为180度，和三个内角的比例关系，∠BAC=135°∠ABC=25°∠ACB=20°∠EAB=∠BAC=135°∠EAC=360°-∠EAB-∠BAC=90°∠DCA=∠ACB=20°所以∠EFC=∠EAC+∠DCA=110°（1）AE=AC，∠ACB=90°，∠ACE=1/2(180°-∠ACB)=...

千问 · 2013-1-24 18:40:28

1, n^2+3n+1=(n+2)*n+n+2-1
=(n+2)(n+1)-1n^2+3n+1=n(n+3)+1(n^2+3n+1)^2=[(n+2)(n+1)-1]*...

千问 · 2013-1-24 18:40:28

1、x=(n2+3n)(n2+3n+2)=[(n2+3n+1)-1]·[(n2+3n+1)+1]=(n2+3n+1)2-1<Y.2、（1）∵∠BAC:∠ABC:∠ACB=27:5:4
∴∠BAC=135°，∠ABC=25°，∠ACB=20°.
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