Question 448604
The area of a parallelogram is equal to the product of the length of one of its sides and the height to that side.

We can draw a line from the top left vertex perpendicular to the bottom, this will create a 90 degree right angle at the bottom ( which we know is 20 )

We have now formed a 45 45 90 triangle, in which we know the hypotenuse to be 5.

Finding the side will give us the height we need for the area calculation.

5 = s{{{sqrt(2)}}}, therefor 5/{{{sqrt(2)}}} = s.
This works out to 5{{{sqrt(2)}}}/2.

Multiply by the length to that side, which is 20,  and we obtain 50{{{sqrt(2)}}}.

Cleomenius.