How do you solve #a^2=4a#?
With quite some care!
Good practise is to re-write it as follows:
And then factor it:
So now you know that you have two solutions, ie
The temptation here, which exists all the way up the maths tree (to my branch, at least!), is to cancel out the
But that just throws away a solution :(
Zero is every bit as scarey as infinity, perhaps even scarier!