Being at a 90 degree angle means that two lines intersect to form a right angle, where both lines are perpendicular to each other and measure 90 degrees.
A 90 degree angle can be measured using a protractor or by using the fact that the sum of the angles in a triangle is 180 degrees, so a right angle would be half of that (90 degrees).
A 90 degree angle is significant in geometry and mathematics as it is one of the basic angles that is used to form other shapes and angles. It is also used in engineering and construction to ensure stability and precision in structures.
Some common examples of a 90 degree angle in the real world include the corners of buildings, the intersection of two roads, and the edges of a book or paper. Other examples include the hands of a clock at 3 and 9 o'clock, and the shape of a square or rectangle.
In trigonometry, a 90 degree angle is used to define the right triangle, which is the basis for many trigonometric functions and calculations. It also helps in determining the relationship between the sides and angles of a triangle, known as the Pythagorean theorem.