How do you solve 13^2=8^2+6^2-2(8)(6)cosA?

2 Answers
Sep 23, 2017

angleA=136^@

Explanation:

"isolate "cosA" by evaluating the numeric values"

rArr169=64+36-96cosA

rArr-96cosA=69

rArrcosA=-69/96=-23/32

rArrA=cos^-1(-23/32)=136^@

Sep 23, 2017

rArrA = 136^o +2kpi" " where k in NN
" "
Or
rArr A=224^o +2kpi" "where k in NN

Explanation:

13^2-8^2-6^2=-2 (8)(6)cosA
" "
rArr169-64-36 =-2 (8)(6)cosA
" "
rArr169-64-36 = -96cosA
" "
rArr 69 = -96cosA
" "
rArrcosA = -69/96
" "
rArr CosA = -0.71875
" "
Since cosA <0" "then A^o in quadrants 2&3
" "
rArrA = 136^o +2kpi" " where k in NN
" "
Or
rArr A=224^o +2kpi" "where k in NN