Squares, each of side 6 cm are cut off from the four corners of a sheet of tin measuring 42 cm by 30 cm. The remaining portion of the tin sheet is made into an open box by folding up the flaps. Find the capacity of the box formed.

If 4 cos² A - 3 = 0 and 0° ≤ A ≤ 90°; find:

(i) angle A

(ii) cos 3 A

(iii) tan² A + cos² A