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kieugiangtran2001
2 năm trước
Vật sáng ab đặc vuông góc với trục chính của thấu kính hội tụ cho ảnh thật a'b'cao 2cm giữ thấu kính cố định dời an lại gần thấu kính một đoạn 45cm thì được ảnh thật a"b" cao 20cm biết khoảng cách giữa hai ảnh thật a'b' và a"b" là 18cm . Hãy xác định: a. tiêu cự của thấu kính . b. Vị trí ban đầu của vật.
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