1. area S = S square = BC = square -EB square =800.

The radical number 2 of BC=20

AC=BD= radical 2BC=400

2.cosA=AC/AB= 1/2 ∠A=60 degrees.

SinB=AC/AB= 1/2 ∠B=30 degrees.

Step 3 be square

Connect EC, FD, MA and NB respectively.

BN passes through EC at G point, and then G, H, T and P are counterclockwise.

Triangle APN is similar to triangle BGE.

AP=BG PN=EG

In the same way.

AP=BG=HC=DT

PN=EG=FH=MT

Then the quadrilateral GHTP is a diamond with four equal sides.

APN is similar to ATD and ADN.

So GPT angle =90 degrees

The quadrilateral GHTP is a square.

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