4x^2 + kxy - 9y^2
how to solve for k?

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?

Extra points! find the missing dimension! need asap

Find the condition that the zeros of the polynomial f(x) = x^3+3px^2+3px+r may be in a. p.