I
An arbitrary term, or placeholder. It is used in general proofs to indicate 'up to whatever desired maximum term'.
Pi ( π ) - used in geometry: ratio of cirle's circumferenct to diameter.Theta (θ) - symbol used in trigonometry, to indicate an angle measurement in degrees.Sigma (Σ) - used in math for summation of a series.Delta (Δ) - used to indicate a change in something.There may be others that I haven't listed. There are many more Greek letters used in the different science fields. Hope that helps.
A protractor can be used to measure an angle.
The instrument used to measure a angle is called a protractor!
I
┴ that one. Sometimes it'll have a small square to indicate a right angle.
An arbitrary term, or placeholder. It is used in general proofs to indicate 'up to whatever desired maximum term'.
When used to indicate angles, "theta" is an unknown (exactly like using "x" for the unknown in equations).
The symbol that you describe seems to be the greek letter Phi. It is normally used to indicate a variable that is an angle, just as x is used to indicate a variable that is a numeric quantity.
You cannot have an angle of less than 0 degrees. In some situations people have defined angles as positive or negative, but this is used to indicate a direction and not size.
A sinometer, or inclinometer, is a device used to measure angles of slope or tilt. To use it, place the sinometer on the surface you want to measure and adjust the device until it indicates the desired angle. You can then take a reading of the angle displayed on the sinometer.
Measurement of the acidity / alkalinity of a food or substance could indicate whether it has the desired charcteristics. This is important in fermentation and other food-making processes.
A set of categories
Yes, litmus is an indicator made from lichens. The dyes extracted from lichens are used to make litmus paper, which is commonly used to indicate the acidity or alkalinity of a solution by changing color.
They used feathers cut at an angle, they diped them in an ink well.
Various types of lenses are used in movies depending on the desired shot. Common lenses include wide-angle for expansive shots, standard for a natural perspective, and telephoto for close-ups or capturing distant subjects. Cinematographers choose specific lenses to achieve the desired visual effect for each scene.