Let x and y be two variables such that xy^2 is a constant. When x is doubled, y is
A--halved.
B--decreased by 18.4%.
C--decreased by 22.5%
D--decreased by 29.3%
Thanks!
中四數學題
2010-08-13 11:02 pm
回答 (1)
2010-08-13 11:13 pm
✔ 最佳答案
Let xy^2 = k where k is a constant. When x is doubled,let the % change of y be r% :2x * [(1+r%)y]^2 = k(2xy^2) (1+r%)^2 = k2k (1+r%)^2 = k(1+r%)^2 = 1/21+r% = √2 / 2r% = √2 / 2 - 1r% = - 0.293 (decreased by 29.3%)(D)
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