a+b+c+d=[(a+b)+d]+c

Solution for a+b+c+d=[(a+b)+d]+c equation:

Simplifying
a + b + c + d = [(a + b) + d] + c

Remove parenthesis around (a + b)
a + b + c + d = [a + b + d] + c

Remove brackets around [a + b + d]
a + b + c + d = a + b + d + c

Reorder the terms:
a + b + c + d = a + b + c + d

Add '-1a' to each side of the equation.
a + b + c + -1a + d = a + b + c + -1a + d

Reorder the terms:
a + -1a + b + c + d = a + b + c + -1a + d

Combine like terms: a + -1a = 0
0 + b + c + d = a + b + c + -1a + d
b + c + d = a + b + c + -1a + d

Reorder the terms:
b + c + d = a + -1a + b + c + d

Combine like terms: a + -1a = 0
b + c + d = 0 + b + c + d
b + c + d = b + c + d

Add '-1b' to each side of the equation.
b + c + -1b + d = b + c + -1b + d

Reorder the terms:
b + -1b + c + d = b + c + -1b + d

Combine like terms: b + -1b = 0
0 + c + d = b + c + -1b + d
c + d = b + c + -1b + d

Reorder the terms:
c + d = b + -1b + c + d

Combine like terms: b + -1b = 0
c + d = 0 + c + d
c + d = c + d

Add '-1c' to each side of the equation.
c + -1c + d = c + -1c + d

Combine like terms: c + -1c = 0
0 + d = c + -1c + d
d = c + -1c + d

Combine like terms: c + -1c = 0
d = 0 + d
d = d

Add '-1d' to each side of the equation.
d + -1d = d + -1d

Combine like terms: d + -1d = 0
0 = d + -1d

Combine like terms: d + -1d = 0
0 = 0

Solving
0 = 0

Couldn't find a variable to solve for.

This equation is an identity, all real numbers are solutions.