kill(all)$

van = facebook.com/LearningCalculus;

f(x,a):=5*cos(x)^2 + sin(x)^2 + 2*(2-a) = 0$

solve(f(x,a),a);

f(x,5/2);

f(x,9/2);

[5/2 <= x and x <= 9/2];