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$$ABC$$ is a triangle and $$AD$$ is its altitude. If $$BD = 5DC$$, then the value of $$\frac{3(AB^2-AC^2)}{BC^2}$$ is
Correct Answer: 2
Since $$AD$$ is the common altitude, $$AB^2-AC^2=BD^2-DC^2$$. Taking $$DC=x$$ and $$BD=5x$$ gives $$BC=6x$$ and $$BD^2-DC^2=25x^2-x^2=24x^2$$. So $$\frac{3(AB^2-AC^2)}{BC^2}=\frac{3(24x^2)}{36x^2}=2$$.
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