呢條題應該點解？
2017/06/21 00:28
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呢條題應該點解？
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最佳解答:
設$x為原價,y為第一次用３６元可買的牛奶數目 xy = 36--------------------------------(1) (x-0.3)(y+4) = 36-------------------(2) 由(1),x = 36/y------------------------(3) 將(3)代入(2) (36/y - 0.3)(y + 4) = 36 (36 - 0.3y)(y + 4) = 36y 36y - 0.3y^2 + 144 - 1.2y = 36y 0.3y^2 + 1.2y - 144 = 0 y = 20 或 y = -24(捨去) ∴小明第一次買了20合牛奶
其他解答:
Let x be the original price,and y be the no. of milk at the first time. then we have, xy=36 x=36/y............(1) (x-0.3)(y+4)=36 xy+4x-0.3y-1.2=36 xy+4x-0.3y=37.2......(2) sub (1) into (2) y(36/y)+4(36/y)-0.3y=37.2 36+144/y-0.3y=37.2 144/y-0.3y=1.2 144-0.3y^2=1.2y 0.3y^2+1.2y-144=0 y^2+4y-480=0 (y+24)(y-20)=0 y=20 or-24(reject) therefore he buy 20 box at the first time.
呢條題應該點解？
發問:
此文章來自奇摩知識+如有不便請留言告知
小明第一次用３６元買了若干合牛奶，第二次買的時候呢個牌子減价，每合便宜０．３元，小明同樣用３６元買這種牛奶，比第一次多買了４合，問小明第一次買了多少合牛奶？ 請幫忙解答，請詳細解析。最佳解答:
設$x為原價,y為第一次用３６元可買的牛奶數目 xy = 36--------------------------------(1) (x-0.3)(y+4) = 36-------------------(2) 由(1),x = 36/y------------------------(3) 將(3)代入(2) (36/y - 0.3)(y + 4) = 36 (36 - 0.3y)(y + 4) = 36y 36y - 0.3y^2 + 144 - 1.2y = 36y 0.3y^2 + 1.2y - 144 = 0 y = 20 或 y = -24(捨去) ∴小明第一次買了20合牛奶
其他解答:
Let x be the original price,and y be the no. of milk at the first time. then we have, xy=36 x=36/y............(1) (x-0.3)(y+4)=36 xy+4x-0.3y-1.2=36 xy+4x-0.3y=37.2......(2) sub (1) into (2) y(36/y)+4(36/y)-0.3y=37.2 36+144/y-0.3y=37.2 144/y-0.3y=1.2 144-0.3y^2=1.2y 0.3y^2+1.2y-144=0 y^2+4y-480=0 (y+24)(y-20)=0 y=20 or-24(reject) therefore he buy 20 box at the first time.
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