What fraction area is shaded ?: twitter got stumped

Shaded region 1

Pic credit : Ed southhall

This question went  viral on twitter,
only a few are able to solve it .

Can you do this?

If not

Sol. Is Below

If you look at the pic you'll see that

Pink triangle is similar to smaller triangle

by AAA(angle,angle,angle) property.

Let Side of square = x = base of pink triangle

=> Side of smaller triangle = x/2

                                                   

                                                 

Let height of pink triangle = h'

  & Smaller triangle= h

As triangles are similar 

 Therefore

   

    x        h'

   ---- =   ---

   x/2      h

h' = 2h

i.e.  h'    

      ---- = h

       2

h'/2 + h' = h +h'

 3/2 h' = x  [ as h+h'= x]

h' = 2/3 x

Area of  triangle      1/2× x ×2/3x

-------------------------  =  ------------------- = 1/3

Area of  square           x × x

[ Area of triangle = 1/2 × base × height]

  Ans:    1/3