Question 983867

{{{a= 31m}}}, 
{{{b=42m}}}, 
{{{c=60m}}}

Use the Cosine Law:

{{{c^2 =  a^2 + b^2  - 2ab*cos(C)}}}

{{{(60m)^2 =  (31m)^2 + (42m)^2  - 2(31m)(42m)*cos(C)}}}

{{{3600m^2 = 961m^2 + 1764m^2  - 2604m^2*cos(C)}}}

{{{3600m^2 = 2725m^2  - 2604m^2*cos(C)}}}

{{{3600m^2 -2725m^2 = - 2604m^2*cos(C)}}}

{{{875m^2 = - 2604m^2*cos(C)}}}

{{{875m^2/- 2604m^2=cos(C)}}}

{{{cos(C)=- 0.3360215053763441}}}

{{{C=109.63466712778866}}}°

{{{C=109.6347}}}°

{{{C=109}}}°{{{38}}}'