Differentiate: 1 - cosx/ 1 +cosx

What is the equation of a line passing through the point (6,1) and parallel to the line whose equation 3x=2y+4

In a graph with several intervals o data how does a constant interval appear? what type of scenario produces a constant interval?

Mat bought a phone for $100. he has to pay $30 per mouth. if he has paid $640 in total, how many mouth has he had the phone?