can the variables be negative ?

i have maximize the function below

z=0.75x1+0.91x2+0.98x3;

subject to

150x1+275x2+310x3<=1000
3.75x1+4.55x2+4.90x3<=1000
150x1+275x2<=500

i tried to find out the value using linpro() function

[x opt]=ling(-c,A,b)
x1= 775.7752
x2=-421.3319
opt=-200

[Image Analyst]

linpro()? But you used ling().

[x opt]=ling(-c,A,b)

[dpb]

If course if there are no bounds specified (as there weren't)

Keep reading the documentation for all the variations -- you need the one at least with

x = linprog(f,A,b,Aeq,beq,lb,ub) defines a set of lower and upper bounds on the design variables, x, so that the solution is always in the range lb ≤ x ≤ ub. Set Aeq = [] and beq = [] if no equalities exist.

to specify the lb array.

Your sample code above is full of typos and missing variables; I didn't try to fix it to be able to run it...