In (bigtriangleup) XYZ, XY = 13cm, YZ = 9cm, XZ = 11cm and XYZ = (theta). Find cos(theta)o
-
A.
(frac{4}{39}) -
B.
(frac{43}{39}) -
C.
(frac{209}{3}) -
D.
(frac{43}{78})
Correct Answer: Option D
Explanation
cos(theta) = (frac{13^2 + 9^2 – 11^2}{2(13)(9)})
= (frac{169 + 81 – 21}{26 times 9})
cos(theta) = (frac{129}{26 times 9})
= (frac{43}{78})