Or the winter vacation math problem of the fifth grade primary school in Xiangyang City, Hubei Province: (How to do this problem in primary school)

Remember learning equations in elementary school?

Let Fe = EB = BD = DF = X.

EC/ED=AE/AF=AC/AB

EC/ED=AE/AF

10/x=8/AF

AF=8x/ 10= 0.8x

AF^2 + FE^2 = AE^2

(0.8x)^2 + x^2 = 8^2

Root (64 * x 2+x 2) = root (8 2)

Root (1.64 * x 2) = 8

Root (1.64) x = 8

X = 8/ root (1.64)

AE/FE= EC /DC

8 / x = 10 / DC

10x = 8 DC

DC = 10x/8

DC = 10 * 8/ (root (1.64)*8)

DC = 10/ root (1.64)

Now that we know all aspects, we can ask for anything we want.

Shadow area = ab * BC/2-x 2 2

= (AF + FB) * (BD + DC)/2 - x^2

=(0.8x+x)*(x+ 10x/8)/2-x^2

= 1.8x * 2.25 x/2 -x^2

= 1.8 * 2.25/2 *x^2 - x^2

= 2.025 x^2 - x^2

= 1.025 x^2

= 1.025 (8/ root (1.64)) 2

= 1.025 * 64 / 1.64

= 40