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6.- All its sides are different so it is a Scalene triangle ( by its sides) also is an acute triangle because its three angles measure less than 90°.
10.- Also is a Scalene triangle and an acute triangle.
5.- It's an Scalene triangle because all its sides have a different length
it's an obtuse triangle because 1 of its angles measure more than 90°.
15.-
8x + 4 + 80 + 3x - 6 = 180
11x + 78 = 180
11x = 180 - 78
11x = 102
x = 102/11
13.- 64 + 27 + 97 + x = 180
x = 180 - 64 - 27 - 97
x = -8
16.-
x + 23 + 80 + 4x + 17 = 180
5x = 180 - 23 - 80 - 17
5x = 60
x = 12
17.- 5x + 10 + 58 + 180 - 11x - 2 = 180
-6x = -10 - 58 + 2
-6x = -68 +2
-6x = -66
x = -66/-6
x = 11