Question
Question: If a line makes the angle a, b, g with three dimensional co-ordinate axes respectively, then cos 2a ...
If a line makes the angle a, b, g with three dimensional co-ordinate axes respectively, then cos 2a + cos2b + cos2g =
A
–2
B
–1
C
1
D
2
Answer
–1
Explanation
Solution
cos2a + cos2b + cos2g
= 2cos2a – 1 + 2cos2b – 1 + 2cos2g – 1
= 2(cos2a + cos2b + cos2g) – 3 = – 1