Use the method of variation of parameters to determine the general solution of the given differential equation. y^(4) + 2y" + y = sin t

Which is the completely factored from of xy^3-x^3y

Tim's phone service charges $26.39 plus an additional $0.21 for each text message sent per month. if tim's phone bill was $31.64, which equation could be used to find how many text messages, x, tim sent last month?

Which is true regarding the graphed function f(x)?