4) Vật sáng AB cao 2cm hình dạng mũi tên, A nằm trên trục chính, AB vuông góc trục chính đặt cách thấu kính hội tụ 45cm, biết tiêu cự của thấu kính là 15cm. Vẽ và nhận ảnh qua thấu kính.

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