It is generally desirable in the context of perceptron learning to have a trainable threshold $s$. Prove that a one-input neuron with a fixed threshold $s=−1$ could not learn to carry out the identity function.
Assuming the input is $x$, is the identity function $x+x= x$ or $x\cdot x = x$ (or am I misunderstanding something here)?
I think the identity function referred to here is f(x) = x