No, not every trapezoid is an isosceles trapezoid.
The altitude of a trapezoid bisects the bases of the trapezoid.
All the names to classify a trapezoid are a trapezoid and a quadrilateral.
A trapezoid can also take the form of an isosceles trapezoid
Concave is a property of [irregular] polygons. A parallelogram cannot be concave.
A trapezoid is convex.
No
It depends entirely on their relative shapes and sizes. They could make a triangle, a parallelogram, a square, or a pentagon or even a concave heptagon.
A big triangle if you put the triangle on the trapezoid's short parallel side, or a parallelogram if you put it on one of the trapezoid's ends. In both cases the triangle must be exactly the right shape and size or you will only have an irregular quadrilateral, pentagon, or hexagon. (Placing an appropriately-sized triangle on the long parallel side will also yield a pentagon - likely irregular.) Additionally, if a vertex of the triangle touches the trapezoid it can also make an irregular concave heptagon!
4-sided polygons include the square, rectangle, and rhombus (all parallelograms), and the trapezoid.*A fifth type is a concave or convex quadrilateral with no equal or parallel sides.
No, not every trapezoid is an isosceles trapezoid.
The altitude of a trapezoid bisects the bases of the trapezoid.
The opposite of convex is concave. Concave shapes have an inward curve, while convex shapes have an outward curve.
All the names to classify a trapezoid are a trapezoid and a quadrilateral.
A trapezoid can also take the form of an isosceles trapezoid
A trapezoid is a polygon. Therefore, a trapezoid has no height
A trapezoid with congruent diagonals is an isosceles trapezoid.