Law of Cosines.
- For a triangle ABC with sides labeled a,b, and c:
[tex]a^2=b^2+c^2-2bc\cos A[/tex][tex]b^2=a^2+c^2-2ac\cos B[/tex][tex]c^2=a^2+b^2-2ab\cos C[/tex]
Since we are asked to look for angle B, we will use
[tex]b^2=a^2+c^2-2ac\cos B[/tex]Given:
a = 12 cm
b = 8 cm
c = 15 cm
Substituting the given values to our equation:
[tex]b^2=a^2+c^2-2ac\cos B[/tex][tex](8)^2=(12)^2+(15)^2-2(12)(15)\cos B[/tex][tex]64=144+225-(360)\cos B[/tex][tex]360\cos B=369-64[/tex][tex]360\cos B=305[/tex][tex]\frac{360\cos B}{360}=\frac{305}{360}[/tex][tex]B=\cos ^{-1}\frac{305}{360}[/tex][tex]B=32.089[/tex]Since we are asked to round the answer to its nearest tenth, the final answer would be 32.1 degrees.