Question

an object is placed at 30cm infront of a concave mirror of focal length 15cm at what distence from the mirror would a screen be placed in order to obtain a sharp image

Answer 1

principal focus is the answer

Answer 2

$\fcolorbox{black}{white}{<strong><em><u>P</u></em></strong><strong><em><u>r</u></em></strong><strong><em><u>i</u></em></strong><strong><em><u>n</u></em></strong><strong><em><u>c</u></em></strong><strong><em><u>i</u></em></strong><strong><em><u>p</u></em></strong><strong><em><u>a</u></em></strong><strong><em><u>l</u></em></strong><strong><em><u> </u></em></strong><strong><em><u>Focus</u></em></strong><strong><em><u>.</u></em></strong><strong><em><u>.</u></em></strong>}$