1) if the point (3,10) is on the graph of y=a^x, then what is this point on the graph of y= log (base a )x?
2) the first terms of a geometric sequence are x, x+5 and x+9. determine the numerical value of the first three terms.
3)in a particular lake the intensity of light is reduced by 3% for each metre that a diver descends below the surface of the water. how far below the surface is the intensity of light only 5% of that at the surface ( answer to the nearest metre)
math question need help
2010-04-04 2:28 pm
回答 (2)
2010-04-04 4:37 pm
✔ 最佳答案
2)(x+5)/x = (x+9)/(x+5)
(x+5)^2 = (x+9)x
x^2 + 10x + 25 = x^2 + 9x
x = -25
-25, -20, -16
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3)
intensity of light at the surface = L
deep at which the intensity of light only 5% of that at the surface = n
L (1 - 3%)^n = 5% L
(1 - 3%)^n = 5%
0.97^n = 0.05
n log 0.97 = log 0.05
n = 98
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i cannot understand the question 1, cannot help you
2010-04-04 6:28 pm
Q1.The 2 graphs r symmetrical about line y = x. Let point on y = log x be (m, n) . So slope of (m,n) and (3,10) = - 1, thus n + m = 13 ....(1) Also mid-point of (m,n) and (3,10) is on line y = x. so (m + 3)/2 = (n + 10)/2 , m - n = 7.....(2) we get m = 10 and n = 3. The point is (10,3)!
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