How does brutus’ tragic flaw of idealism contribute to his downfall?

Brutus' tragic flaw of idealism contributes to his downfall because he was gullible enough to be convinced by Cassius and Antony that they were going to murder Julius Caesar for Rome's development and goodwill.

Only if that could happen to everyone

substitute y = 2x - 4 to x + 2y = 12:

x + 2(2x - 4) = 12     use distributive property

x + (2)(2x) + () = 12

x + 4x - 8 = 12     add 8 to both sides

5x = 20     divide both sides by 5

x = 4

put the value of x to the first equation:

y = 2(4) - 4

y = 8 - 4

y = 4

answer: x = 4 and y = 4