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## Answers

angle a=90degree

rtp: abcd is a square

construction:db is joined

proof:in triangle adb &bcd

ad=bc

bd is the common arm

&abd=alternate angle bdc

so triangle abd congruent bcd(sas)

therefore,ab=dc(cpct)

so,in the parralelogram abcd the four sides are equal

therefore abcd is a square

THUS PROVED

to prove : abcd is a square

proof: in triangles abd and bcd,

ad=bc- s

cdb=dba-a(alternate angles)

ab=dc -s

by sas congruence rule triangle abd≈bcd.

since two pair of opposite sides are equal and one angle is 90, it is a square