Sometimes a change of variable can be used to convert a differential equation y′=f(t, y) into a separable equation. one common change of variable technique is as follows. consider a differential equation of the form y′=f(αt+βy+γ), where α,β, and γ are constants. use the change of variable z=αt+βy+γ to rewrite the differential equation as a separable equation of the form z′=g(z). solve the initial value problem y′=(t+y)2−1, y(3)=4.