Step-by-step explanation:
1). 6, 9, 10
6²+9² =
36+81 = 117
10² = 100
6²+9² > 10²
the acute triangle
2). 2, 12, 13
2²+12² =
4+144 = 148
13² = 169
2²+12² < 13²
the obtuse triangle
3). 9, 12, 19
9²+12²=
81+ 144 = 225
19² = 361
9²+12² < 19²
the obtuse triangle
4). 21, 28, 35
21²+28² =
441 + 784 = 1,225
35² = 1,225
21²+28² = 35²
the right triangle
