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algebra intermediate

Problem

A line that passes through the origin intersects both the line and the line . The three lines create an equilateral triangle. What is the perimeter of the triangle?
(A)
(B)
(C)
(D)
Solution
Since the triangle is equilateral and one of the sides is a vertical line, the triangle must have a horizontal line of symmetry, and therefore the other two sides will have opposite slopes. The slope of the other given line is (which is must be, given 60 degree angle of the triangle, relative to vertical) so the third must be . Since this third line passes through the origin, its equation is simply . To find two vertices of the triangle, plug in to both the other equations. We now have the coordinates of two vertices, and . The length of one side is the distance between the y-coordinates, or . The perimeter of the triangle is thus , so the answer is
Final answer
D