strange wrote:

E. 40

2*(side1)^2 = 21^2

2*(side2)^2 = 19^2

since side^2 = area,

(side1)^2 - (side2)^2 = 0.5 * (21-19) * (21 + 19) = 40

Is what you wrote.. .

Could you please explain as to how u arrived at this formula.. I did get the answer, but i guess mine was a more circuitous way?

thanks!!

Let the sides of the larger screen be x, then (2x^2) = 21^2-> x^2 = 21^2/2

Let the sides of the smaller screen be y, then (2y^2) = 19^2-> y^2 = 19^2/2

Difference = (21^2 - 19^2)/2 = [(21+19)(21-19)]/2 = 40(2)/2 = 40

Do you know pythagoras theroem? It's what the formulas used here are based on.