A kite
depending if its octagon regular, or irregular (sides arent equal angles arent equal
A parallelogram
The shape you are describing is a rhombus. A rhombus has two pairs of parallel sides, with opposite sides being equal in length. The diagonals of a rhombus are also equal in length, but they do not intersect at 90 degrees; instead, they intersect at a 90-degree angle.
A parallelogram (or rectangle) which is not a rhombus (or square).
A rectangle would fit the given description
When two perpendicular lines cross you get four equal angles of 90 degrees.
No. A cross product is just a way of simplifying a proportion. If the cross product aren't equal, it follows logically that the proportion isn't equal.
41 degrees Fahrenheit is equal to 5 degrees Celsius.
0 degrees C is equal to 32 degrees F
Negative 1.6 degrees Celsius is equal to about 29.12 degrees Fahrenheit.
60 degrees Celsius is equal to 140 degrees Fahrenheit.