## Elementary Geometry for College Students (6th Edition)

using theorem 11.4.3 Law of cosine a=6,b =10, c=8 $b^{2}$ = $a^{2}$ + $c^{2}$ - 2ac cos β $10^{2}$ = $(6)^{2}$ + $(8)^{2}$ - 2*6*8*cos β 100 = 36+64 - 96cos β 96cos β = 36 +64 -100 96cos β = 0 cos β = 0 β = $cos^{-1}$(0) β = 90°