Orthogonal complements- P+Q

Question

Suppose P is the orthogonal projection onto a subspace E, and Q is the orthogonal projection onto the orthogonal complement E⊥.

a) What is P+Q?

I am a little unsure of how to do this. I know the answer is I. I know P is the transformation on E and Q is the transformation on E⊥. I feel like the proof should be relatively simple but I just can't figure how to go about it/ start.

Answer 1

We have $Q=I-P$. Try to show this !