In triangle [math]ABC:\:|AB|=|AC|,\:\angle BAC=100^{\circ}[/math]. Let [math]D[/math] be a point such that [math]B[/math] is an interior point of [math]AD[/math] and [math]|AD|=|BC|[/math]. How can you find [math]\:\angle BDC\:[/math]?
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