Answer:
The side c needs to be 12.85 for the triangle to have greatest perimeter
Step-by-step explanation:
We are given;
b = 13
a = 15
Angle at b: B = 55°
Let's find side c.
Using the law of cosines,we have;
b² = a² + c² - 2ac•cos(B)
13² = 15² + c² - 2•15•c•cos(55)
169 = 225 + c² - 30c•cos(55)
c² - 30c•cos(55) + 225 - 169 = 0
c² - 30c•cos(55) + 56 = 0
c² - 30c•(0.5736) + 56 = 0
c² - 30c•(0.5736) + 56 = 0
c² - 17.208c + 56 = 0
Using quadratic formula;
c = [-(-17.208) ± √((-17.208)² - (4•1•56)]/2(1)
c = [17.208 ± √(296.115 - 224)]/2
c = 8.604 ± 4.246
To have the greater perimeter, we need the larger value of c, thus we will use the positive sign and ignore the negative one ;
Thus,
c = 8.604 + 4.246 = 12.85
