Thanks, I solve it,

clc

clear

syms a b x y c1 c2 c3 c4 T1 T2 T3 T4

T=c1+c2*x+c3*y+c4*x*y;

r1=c1+c2*a+c3*b+c4*a*b-T1;

r2=c1-c2*a+c3*b-c4*a*b-T2;

r3=c1-c2*a-c3*b+c4*a*b-T3;

r4=c1+c2*a-c3*b-c4*a*b-T4;

p13=r1+r3;

p24=r2+r4;

n1=solve(p13==0,c1);

n2=solve(p24==0,c1);

C4=solve(n1==n2,c4)

w1=solve(p13==0,c4);

w2=solve(p24==0,c4);

C1=solve(w1==w2,c1)

r1=subs(r1,c1,C1);

r1=subs(r1,c4,C4);

r2=subs(r2,c1,C1);

r2=subs(r2,c4,C4);

r3=subs(r3,c1,C1);

r3=subs(r3,c4,C4);

r4=subs(r4,c1,C1);

r4=subs(r4,c4,C4);

q12=r1+r2;

q34=r3+r4;

C3=solve(q12==0,c3)

r1=subs(r1,c3,C3);

r2=subs(r2,c3,C3);

r3=subs(r3,c3,C3);

r4=subs(r4,c3,C3);

C2=solve(r1==0,c2)

r1=subs(r1,c2,C2);

r2=subs(r2,c2,C2);

r3=subs(r3,c2,C2);

r4=subs(r4,c2,C2);

C1

C2

C3

C4

## Best Answer