1988 AIME Problems/Problem 11
Let be complex numbers. A line in the complex plane is called a mean line for the points if contains points (complex numbers) such that For the numbers , , , , and , there is a unique mean line with -intercept 3. Find the slope of this mean line.
Each lies on the complex line , so we can rewrite this as
Matching the real parts and the imaginary parts, we get that and . Simplifying the second summation, we find that , and substituting, the answer is .
We know that
And because the sum of the 5 's must cancel this out,
We write the numbers in the form and we know that
The line is of equation . Substituting in the polar coordinates, we have .
Summing all 5 of the equations given for each , we get
Solving for , the slope, we get
The mean line for must pass through the mean (the center of mass) of these points, which, if we graph them on the complex plane, is . Since we now have two points, namely that one and , we can simply find the slope between them, which is by the good ol' slope formula.
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