Question

Consider the figure shown below. How long is DE?

Answer 1

c).
`2√(2)`

Explanation:

It's a right triangle with equal sides (DE == EF).

We know that

`4^2 = DE^2 + EF^2 = 2\cdot DE^2\\16 = 2\cdot DE^2\\8 = DE^2\\4\cdot2 = DE^2\\2√(2) = DE\textrm{; because }-2√(2) = DE\textrm{ doesn't make sense in geometry}`