Processing Math: Done
To print higher-resolution math symbols, click the
Hi-Res Fonts for Printing button on the jsMath control panel.

jsMath
發新話題
打印

2010TRML

abcd為等差數列,且實數xyzw滿足a+b+c+d=50x+y+z+w=10ax+by+cz+dw=100,則aw+bz+cy+dx=?(2010TRML團體賽)
[解答]
假設a1為首項,t為公差,a=a13tb=a1tc=a1+td=a1+3t

a+b+c+d=50(a13t)+(a1t)+(a1+t)+(a1+3t)=50a1=225

ax+by+cz+dw=100(a13t)x+(a1t)y+(a1+t)z+(a1+3t)w=100
a1(x+y+z+w)+(3txty+tz+3tw)=100 , a1=225代入得3tx+tytz3tw=25

aw+bz+cy+dx=(a13t)w+(a1t)z+(a1+t)y+(a1+3t)x=(3tx+tytz3tw)+a1(w+z+y+x)=150

[ 本帖最後由 bugmens 於 2011-2-26 09:16 PM 編輯 ]

TOP

發新話題