Trigonometric EquationHard
Question
If x = y cos 
= z cos 
, then xy + yz + zx =
= z cos , then xy + yz + zx = Options
A.-1
B.0
C.1
D.2
Solution
x = y cos (π - 
) = z cos (π + 
)
= -y cos
= -z cos 
⇒ xy + yz + zx = (1) (-2) + (-2) (-2) + (-2) (1)
= -2 + 4 - 2 = 0
) = z cos (π + )= -y cos
= -z cos ⇒ xy + yz + zx = (1) (-2) + (-2) (-2) + (-2) (1)
= -2 + 4 - 2 = 0
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