A square has a diagonal of 16. What is the side length of the square?

Can someone answer it, and plot it, for 20 points and brainliest answer? p. s. they're the same ! : )

16 more than the product of 5 and p

I’ve been trying all day to figure this puzzle out. i need the work for it aswell. it is a factoring polynomials tarsia. the image is below.