我现在需要解一个含字母的方程组，写的代码为

[x,y]=solve('lac*cos(a0-a1)+lab*cos(a2)-lcd-lbd*cos(a3)','lac*sin(a0-a1)+lab*sin(a2)-lbd*sin(a3)',a2,a3);

式中除了a1,a2,a3为未知量，其余均为已知量，方程目的是将a2,a3用a1表示出来，但是这个代码用matlab解出来为a2:[0x1 sym] a3：[0x1 sym]

将方程中的已知量换为数字后

[x,y]=solve('154.35*cos(1.1361-a1)+520*cos(a2)-650-154.35*cos(a3)','154.35*sin(1.1361-a1)+520*sin(a2)-154.35*sin(a3)',a2,a3);

就能够得出解

x =

2.0*atan((2508359.0*tan(0.5*a1 - 0.56805) - (1710159.0*(1058841.0*tan(0.5*a1 - 0.56805) - 1300.0*(-1.0*(1643.0*tan(0.5*a1 - 0.56805)^2 - 1787.0)*(4387.0*tan(0.5*a1 - 0.56805)^2 + 957.0))^(1/2)))/(1690000.0*tan(0.5*a1 - 0.56805)^2 - 1710159.0) + (1690000.0*tan(0.5*a1 - 0.56805)^2*(1058841.0*tan(0.5*a1 - 0.56805) - 1300.0*(-1.0*(1643.0*tan(0.5*a1 - 0.56805)^2 - 1787.0)*(4387.0*tan(0.5*a1 - 0.56805)^2 + 957.0))^(1/2)))/(1690000.0*tan(0.5*a1 - 0.56805)^2 - 1710159.0))/(19223100.0*tan(0.5*a1 - 0.56805)^2 + 11196900.0))

2.0*atan((2508359.0*tan(0.5*a1 - 0.56805) - (1710159.0*(1058841.0*tan(0.5*a1 - 0.56805) + 1300.0*(-1.0*(1643.0*tan(0.5*a1 - 0.56805)^2 - 1787.0)*(4387.0*tan(0.5*a1 - 0.56805)^2 + 957.0))^(1/2)))/(1690000.0*tan(0.5*a1 - 0.56805)^2 - 1710159.0) + (1690000.0*tan(0.5*a1 - 0.56805)^2*(1058841.0*tan(0.5*a1 - 0.56805) + 1300.0*(-1.0*(1643.0*tan(0.5*a1 - 0.56805)^2 - 1787.0)*(4387.0*tan(0.5*a1 - 0.56805)^2 + 957.0))^(1/2)))/(1690000.0*tan(0.5*a1 - 0.56805)^2 - 1710159.0))/(19223100.0*tan(0.5*a1 - 0.56805)^2 + 11196900.0))

y =

-2.0*atan((1058841.0*tan(0.5*a1 - 0.56805) - 1300.0*(-1.0*(1643.0*tan(0.5*a1 - 0.56805)^2 - 1787.0)*(4387.0*tan(0.5*a1 - 0.56805)^2 + 957.0))^(1/2))/(1690000.0*tan(0.5*a1 - 0.56805)^2 - 1710159.0))

-2.0*atan((1058841.0*tan(0.5*a1 - 0.56805) + 1300.0*(-1.0*(1643.0*tan(0.5*a1 - 0.56805)^2 - 1787.0)*(4387.0*tan(0.5*a1 - 0.56805)^2 + 957.0))^(1/2))/(1690000.0*tan(0.5*a1 - 0.56805)^2 - 1710159.0))

请问怎么样使方程中的已知量用字母表示时也能求出方程的解？