One.
Just one
It depends on the type of triangle. A scalene triangle (no equal sides) has no rotational symmetry. An isosceles triangle (2 equal sides) has rotational symmetry order 2. An equilateral triangle (3 equal sides) has rotational symmetry order 3. The order of rotational symmetry is how many time a shape will fit over itself during one complete rotation.
A trapezium has normally no lines of symmetry unless it is an isosceles trapezium which has 1 line of symmetry
it has only one line of symmetry.
180* or 120*, not sure
If it is an isosceles trapezoid, then there is only one line of symmetry, right down the middle of it from top to bottom. If it is a plain old trapezoid with no congruent sides, then there are no lines of symmetry.
180 degrees, like all triangles.
There could be almost any acute angle. it maters what kind it is
ALL triangles - have internal angles that add up to 180 degrees.
They're free, use as many as you want. It would help for you to tell us what specific object you're asking about.
The angles inside any triangle sum to 180 degrees. Isosceles simply means two sides are the same length.
iscosolese triangle: 2 congruent sides and one that is not congruent Scalene: all un congruent equaladeral: all congruent