*An occasional series highlighting common errors that refuse to die.*

“It just… won’t stay dead!” he said, as the Mathematical Zombie moved closer.

“$(a+b)^2 = a^2 + b^2$”, it said. “Brains! $(a+b)^2 = a^2 + b^2$.”

“But… it doesn’t!” he said. “You have to multiply out the brackets!”

“$(a+b)^2 = a^2 + b^2$!”

“No! $(a+b)^2 = (a+b)(a+b) = a^2 + 2ab + b^2$”, he said, firmly.

“Oh,” said the Mathematical Zombie. “So you have to write both brackets down and multiply them out? $a^2$... $ab$... another $ab$... and $b^2$... makes $a^2 + 2ab + b^2$!”

While the Mathematical Zombie was distracted, he shot it in the head.

## Colin

Colin is a Weymouth maths tutor, author of several Maths For Dummies books and A-level maths guides. He started Flying Colours Maths in 2008.
He lives with an espresso pot and nothing to prove.

## MathbloggingAll

The Attack of the Mathematical Zombie: $(a+b)^2$ http://t.co/Rn9edYZgLG

## srcav

This misconception irks me too @icecolbeveridge http://t.co/7MTC5q9pUF

## singinghedgehog

(x+4)/x = 4; “just cross out the x’s” it said.

“reload”

## Colin

Good one, I’ll set them loose on it soon!