Which is less likely to be reliable source of information, the webpage of a university or the webpage of a scientist who is trying to sell a new invention explain

What is the frequency of a light wave with a wavelength of 620nm

We all use gps today, even if we don't drive yet. i bet you have been in the car with a parent and they have asked you to get out your phone to find a specific location. in your car, on the phone, you are using a very sophisticated technology. gps satellites circle the earth twice a day in a very precise orbit and transmit signal information to earth. gps receivers take this information and use trilateration to calculate the user's exact location. essentially, the gps receiver compares the time a signal was transmitted by a satellite with the time it was received. the time difference tells the gps receiver how far away the satellite is. now, with distance measurements from a few more satellites, the receiver can determine the user's position and display it on the unit's electronic map. what type of signal is utilized by the gps satellite?

Aparticle moves in a circle 1.50 m in radius . through what angle in radians does it rotate if it moves through an arc length of 2.50m? what is the angle in degrees?