Mathematics in the second volume of Senior One tells us how to draw rotating figures. Rotate △ ABC 30 counterclockwise around point B to draw a rotated triangle.

Make an equilateral triangle on the left of AB. Remember another point as d, make the midpoint e of AD, and take a point f on the straight line be so that BF=BA. . . . After rotation, the corresponding point f of a is obtained. . .

Similarly, make an equilateral triangle with BC as the side, and get the H point corresponding to point C. .

Connecting BHF is a necessary triangle. . .

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