Question 414262
c= {{{(2cd)/(a-d)}}}, for d 
Multiply both sides by (a-d)
c(a-d) = 2cd
:
multiply inside the brackets by c
ca - cd = 2dc
;
We can simplify this, divide thru by c
a - d = 2d
:
add d to both sides
a = d + 2d
a = 3d
:
divide both sides by 3
d = {{{a/3}}}