First One
f(x)=c-x
f(x)=c/x
f(x)=  (c_(1- ) x)/(c_(2  ) x+1)
f(x)=1/2 (√(c_1^2+ c_2-4 x^2+c_(1 ) x))
f(x)=∛(c-x^2 )

Second One

H[1]: = Solve [{y_(1 )= Y/K,   Y^1>0 ,Y>0,K<0},y]
H[1]: = Solve [{y_(1 )= Y/K,   Y^1>0 ,Y>0,K<0},y]

H[1]: = Solve [{y ̂= Y/K,y ̂   >0 ,y>0,k<0},y]
H[1]: = Solve [{y ̂= Y/K,y ̂   >0 ,y>0,k<0},y]