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1994 AIME Problems/Problem 8

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Problem

The points , , and are the vertices of an equilateral triangle. Find the value of .

Solution

Consider the points on the complex plane. The point is then a rotation of degrees of about the origin, so:

(a+11i)\left(\text{cis}\,60^{\circ}\right) = (a+11i)\left(\frac 12+\frac{\sqrt{3}i}2\right)=b+37i.

Equating the real and imaginary parts, we have:

\begin{align*}b&=a/2-11\sqrt{3}/2 \\37&=11/2+a\sqrt{3}/2 \end{align*}

Solving this system, we find that . Thus, the answer is .

See also

1994 AIME (ProblemsResources)
Preceded by
Problem 7
Followed by
Problem 9
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
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