Question

In ∆JKL, j=7.9inches, k=2 inches and l =9.8. find the measure of

Answer 1

By cosine rule,

$\cos K=\frac{j^2+l^2-k^2}{2jl}$

Where j = 7.9 inch, k = 2 inch and l = 9.8

$\cos K=\frac{7.9^2+9.8^2-2^2}{2\times7.9\times9.8}=\frac{154.45}{154.84}=0.99748$$\begin{gathered} \cos K=0.99748 \\ K=\cos ^{-1}0.99748=4.067\approx4^o \end{gathered}$

Solution: The measure of angle K is 4 degrees