I went through the faq which suggests the following way to achieve what I want:
Code: Select all
""3(x+4)-2(x-1)=3 x+12-(2 x-2) newline
""phantom {3(x+4)-2(x-1)}=3 x+12-2 x+2 newline
""phantom {3(x+4)-2(x-1)}=x+14
""phantom {3(x+4)-2(x-1)}={a} over {abc}
When using the matrix approach I have a similar problem.