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< async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"> 數學問題 (10點)

發問:

(a) IF -8 ,x ,y , 7 are in Arithmetic Progression , find X and Y (b) IF 5, x ,y ,320 are in Geometric Progression find X and Y

最佳解答:

1.-8, x, y. 7 7-y = y-x .... (1) y-x = x-(-8) y-x = x+8 .... (2) from (2) y-8 = 2x x = (y-8)/2 sub into (1) 7-y = y - (y-8)/2 14 - 2y = 2y - y + 8 14 - 8 = 2y - y + 2y 6 = 3y y = 2 sub into ( y-8 = 2x ) 2-8 = 2x -6 = 2x x = -3 -8, -3, 2, 7 2013-12-01 16:18:06 補充： 2. x/5 = y/x = 320/y x2 = 5y ..... (1) y2 = 320x .... (2) from (1) y = x2/5 sub into (2) x?/25 = 320x x3 = 8000 x = 20 y = 80 2013-12-01 17:07:53 補充： The series is 5, 20, 80, 320

其他解答:4E350C6F8B48ECA2