【r18381】評論
已知a70－a57＜0 所以d<0甲：a38－a83＞0(0) (a1+37d)-(a1+82d)=-45d 又d<0 所以-45d>0乙：a43－a51＜0(X) (a1+42d)-(a1+50d)=-8d -8d>0 丙：a28＋a41＞a11＋a58 (X) (a1+27d)+(a1+40d)=2a1+67d (a1+10d)+(a1+27d)=2a1+37d(2a1+67d)-(2a1+37d)=30d<0丁：a12＋a31＝a9＋a34 (O)(a1+11d)+(a1+30d)=2a1+41d(a1+8d)+(a1+33d)=2a1+41d故選 甲丁