解方程4a+6d=26和a.a+3a.d+2d.d=40

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解方程4a+6d=26和a.a+3a.d+2d.d=40

解方程4a+6d=26和a.a+3a.d+2d.d=40
解方程4a+6d=26和a.a+3a.d+2d.d=40

解方程4a+6d=26和a.a+3a.d+2d.d=40
4a+6d=26; a+3d/2=13/2; a=13/2-3d/2
a^2+3ad+2d^2=40; (a+2d)(a+d)=40;
(13/2-3d/2+2d)(13/2-3d/2+d)=40;
(13/2+d/2)(13/2-d/2+)=40;
169/4-d^2/4=40
d^2=9; d=3; d=-3;
a=2; a=11
所以方程的解为:a=2,d=3;或:a=11,d=-3