Find the value of each variable write your answers in the simplest radical form

Use the matrix-column representation of the product to write each column of ab as a linear combination of the columns of a.

International calls require the use of a country code. many country codes a 3-digit numbers. country codes do not begin with a 0 or 1. there are no restrictions on the second and third digits. how many different 3-digit country codes are possible?

Look at this pattern ; 1,4,9, number 10000 belongs in this pattern . what’s the place of this number?