Question: how can i find feasible ranges?

hello everybody, the below expression has 5 variabes: t,c,theta[1],lambda,a and i want to know in what ranges of variables the expression is positive. how can i do that?

y:=2*t*(((-(1/2)*theta[1]+1)*c^2+((1/2-(1/2)*theta[1])*t+a)*c-(1/2)*t^2)*lambda^3+((-3*theta[1]*(1/2)+2)*c^2+((7/2-4*theta[1])*t+2*a)*c+3*t*((-(1/2)*theta[1]+1/6)*t+a))*lambda^2+((-3*theta[1]*(1/2)+1)*c+(-2*theta[1]+1/2)*t+a)*(3*t+c)*lambda-(1/2)*(3*t+c)*(c*theta[1]+t*(3*theta[1]-1)))/((-2*t*lambda^2+(3*t+c)*lambda+c+3*t)*(lambda*c+3*t+c)*(lambda+1))

i use solve() to find these ranges but it takes to much time. is there any alternative solution?

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