Assume that one has an equation P(a,b,c,d,e,f)=0. How do we solve this equation so that the parameters b and c are in terms of a, and the parameters d and e in terms of f?

I have some problems about plotting in Maple.

Question1. I have tried to plot this function for different intervals, but there is no resulting graph.

plot(1+18*(sinh(9*x-9)-sinh(3*x-477))^2/(9*cosh(9*x-9)+cosh(3*x-477))^2,x=-4..4);

What do you think why this happens?

Question2. plot(1+18*(sinh(9*x-9/2)-sinh(3*x-477/2))^2/(9*cosh(9*x-9/2)+cosh(3*x-477/2))^2,x=-1..1);

The graph of this function is a wierd one. Is there any problem?

I am using Maple 15, and before that Maple 8 and Maple 13. While using the versions 13 and 15, 

I come across with this problem; I cannot copy an output and use it as input. In Maple 8, I was able to do this but in 

these improved versions, it seems that it is not possible. Is there a way to solve this problem? I saw some answers about this

problem suggesting to change launch.ini file. But I could not apply this suggestion, since it is not permitted by the system. 

Assume that I have r:= -6x+3y+23x²-4xyz+7z² . By using coeffs(r,x,'k') I can find the coefficients of 1, x, and x². 

What should I write to get the conditions that make the coefficient of x zero? How can I just pick the coefficient of x, and solve it. 

I have several coefficients but the answer of this question will help me. 

Thanks.