Two corners of a triangle have angles of (3 pi )/ 8 and ( pi ) / 6 . If one side of the triangle has a length of 14 , what is the longest possible perimeter of the triangle?

1 Answer
Jan 20, 2017

Longest possible perimeter of the triangle is 67.63

Explanation:

As the two angles of a triangle are (3pi)/8 and pi/6,

the third angle is pi-(3pi)/8-pi/6=(24pi-9pi-4pi)/24=(11pi)/24

As the smallest angle is pi/6, the perimeter will be longest, if the given side 14 is opposite it. Let it be a=14 and other two sides be b and c opposite angles of (3pi)/8 and (11pi)/24.

Now according to sine formula,

a/sinA=b/sinB=c/sinC

i.e. b/sin((3pi)/8)=c/sin((11pi)/24)=14/sin(pi/6)=14/(1/2)=28 and then

b=28sin((3pi)/8)=28xx0.9239=25.8692

and c=28sin((11pi)/24)=28xx0.9914=27.7592

and perimeter is 14+25.8692+27.7592=67.6284~~67.63