SOLUTION: Two numbers differ by 6 and their reciprocals differ by 8/15.Find the numbers

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Question 132604: Two numbers differ by 6 and their reciprocals differ by 8/15.Find the numbers
Answer by solver91311(24713) About Me  (Show Source):
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First number: x
Second number: y

The two numbers differ by 6: x-y=6 We'll just assume that x%3Ey

The reciprocal of the first number: 1%2Fx, x%3C%3E0 and because of x-y=6, y%3C%3E-6
The reciprocal of the second number: 1%2Fy, y%3C%3E0 and because of x-y=6, x%3C%3E6


Their reciprocals differ by 8/15: Since we have assumed that x%3Ey, 1%2Fx%3C1%2Fy, so 1%2Fy-1%2Fx=8%2F15

Re-write the first equation to solve it for x:
x=y%2B6

Substitute this expression for x into the second equation in place of x.
1%2Fy-1%2F%28y%2B6%29=8%2F15

Multiply both sides by 15:
15%2Fy-15%2F%28y%2B6%29=8

Lowest common denominator is just the product of the two denominators since there are no common factors. So:

%2815%28y%2B6%29-15y%29%2F%28y%28y%2B6%29%29=%288y%28y%2B6%29%29%2F%28y%28y%2B6%29%29

Distribute and collect like terms all on the left:
%28-8y%5E2-48y%2B15y%2B90-15y%29%2F%28y%28y%2B6%29%29
%28-8y%5E2-48y%2B90%29%2F%28y%28y%2B6%29%29

Solve the numerator expression for 0, remembering to exclude 0 and -6 as values not in the domain of the function in terms of y.

-8y%5E2-48y%2B90=0

Divide by -2:
4y%5E2%2B24y-45=0

Factor:
%282x-3%29%282x%2B15%29=0, so y = 1.5 or y = -7.5

y = 1.5 => x = 7.5 because 7.5-1.5=6, so:

1%2F1.5-1%2F7.5=5%2F7.5-1%2F7.5=4%2F7.5=8%2F15 and the first root checks.

y = -7.5 => x = -1.5 because -1.5-%28-7.5%29=6, so:

1%2F%28-7.5%29-1%2F%28-1.5%29=-1%2F7.5%2B5%2F7.5=4%2F7.5=8%2F15 and the second root checks.