A hall has space diagonal PQ = 14 m and floor diagonal PR = 6√5 m. If α is the angle between the line joining P and Q, and the line joining P and R, then what is cos α equal to?
A.2√5/7
B.3√5/7✓ Correct
C.1/3
D.2/3
Explanation
PR is on the floor (length 6√5), PQ is the space diagonal (length 14). The angle between them: PR is the projection of PQ onto floor. cos α = PR/PQ = 6√5/14 = 3√5/7.
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