Question 382794
Use the cosine law for the longest side of the triangle:
{{{9^2 = 4^2 + 7^2 - 2*4*7cosA}}}, where A is the angle opposite the side of length 9.  
81 = 16 + 49 - 56cosA;
16 = -56cosA;
cosA = -16/56 = -2/7;
A = 106.6 degrees (approximately)
Therefore the triangle is an obtuse triangle.