Question

State if the three numbers can be the measures of the sides of a triangle. 12, 18, 9

Answer 1

Triangle ABC

Apply rule of Cosin

If 12^ + 9^2 - 2•12•9 Cos X= 18^2

Then

144+ 81 - 216CosX = 324

CosX = (324 -225)/(-216) = 99/-216

CosX = -0.46

Then answer is YES, its a triangle because CosX only have values

between -1 and 1, and -0.46 is between them