Consider the three points P1(1,2,0), P2(3,6,20) and P3(2,4,6) and a view point C(0,0,-10). Choose the correct options.

(A) P1 obscure P2, if viewed from C.

(B) P2 obscure P1, if viewed from C.

(C) P3 does not obscure P1 if viewed from C.

(D) P2 does not obscure P3 if viewed from C.

1. A(A), (B) and (C) Only
2. B(A), (C) and (D) Only
3. C(B), (C) and (D) Only
4. D(A), (B) and (D) Only

Pick an option to check yourself, or open the answer below.

Show answer & explanation

Correct answer: B. (A), (C) and (D) Only

Explanation

The line from C(0,0,−10) through P1(1,2,0) is (t, 2t, −10 + 10t); at t = 3 it passes through P2(3,6,20), so P1 (nearer) obscures P2. P3(2,4,6) is not on it (t = 2 gives z = 10), so P3 does not obscure P1 and P2 does not obscure P3. A, C and D are correct.