C1 = -4 ((am*br +
ar*\[Theta] - (bm*br - \[Theta]^2)*c)*(br + \[Theta])*
g*(8 bm*br + \[Theta]^2)
+ (ar - (br - \[Theta])*c)*(bm*br - \[Theta]^2)*g*4 bm*
br)/((8*bm*br + \[Theta]^2)*(br + \[Theta])^2*g^2 -
4 bm*br*(bm*br - \[Theta]^2)*g^2))) +
1/(4 br*(bm*br - \[Theta]^2) -
2 (br + \[Theta])^2*g^2 - (bm*br - \[Theta]^2)*g^2)*
g*((2 (am*br +
ar*\[Theta] - (bm*br - \[Theta]^2)*c)*(br + \[Theta])*
g + (ar - (br - \[Theta])*c)*(bm*br - \[Theta]^2)*g))
C2 = 3 (ar - (br - \[Theta])*c);
Reduce[C1 < C2 && am > 0 && ar > 0 && 0 < bm < 1 &&
0 < br < 1 && \[Theta] < bm && g < bm && c > 0 &&
am > (bm - \[Theta])*c && ar > (br - \[Theta])*c]

c1的分母括号不匹配