For Anyone who knows anything about Trigonometry, parallelograms I have what appears to be a simple question?

I have a question that appears easy but I can't quite get my head around it. It's a standard Parallelogram with points A - D starting from the bottom right corner (A) moving anticlockwise. The question asks to Express BD in terms of BC and CD. Essentially use 2 sides of a valueless traingle not at 90 degrees to express the hypotenuse? Any help will be Excellent! Thanks