ABCD乘9等于DCBA,可以用算式写为:
(1000A + 100B + 10C + D)* 9 = 1000D + 100C + 10B + A
化简 ,得
8999A + 890B - 10C - 991D = 0
要使一个四位数乘以9后,仍然为四位数,只能是 A = 1,B = 0
代入上式,试算可得:C = 8,D = 9
所以,ABCD=1089
ABCD乘9等于DCBA,可以用算式写为:
(1000A + 100B + 10C + D)* 9 = 1000D + 100C + 10B + A
化简 ,得
8999A + 890B - 10C - 991D = 0
要使一个四位数乘以9后,仍然为四位数,只能是 A = 1,B = 0
代入上式,试算可得:C = 8,D = 9
所以,ABCD=1089