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
\(\frac{43}{78}\)
Verified Correct Answer: D.
Step-by-Step Mathematical Solution
cos\(\theta\) = \(\frac{13^2 + 9^2 - 11^2}{2(13)(9)}\)
= \(\frac{169 + 81 - 21}{26 \times 9}\)
cos\(\theta\) = \(\frac{129}{26 \times 9}\)
= \(\frac{43}{78}\)
Source: Myschool Past Questions Archive (Record #32244)