1) 1탄 : https://zep.us/play/2moZkK (직사각형의 넓이)
2) 2탄 : https://zep.us/play/Dw1GNn (평행사변형의 넓이)
3) 3탄 : https://zep.us/play/ykGZpa (삼각형의 넓이)