Solve the Cauchy Euler equations given below

a$)x^2{y}^{\text{'}\text{'}}+x{y}^{\text{'}}+4y=0$

b$)x^2{y}^{\text{'}\text{'}}+x{y}^{\text{'}}+9y=0,y(1)=0,y^{\text{'}}(1)=2\mathrm{.}5$

c$)x^2{y}^{\text{'}\text{'}}-3x{y}^{\text{'}}+4y=0,y(1)=-,y^{\text{'}}(1)=2$