MR-692 / 12. problem

The bases of the trapezoid are 142 cm and 89 cm, and the diagonals are 120 cm and 153 cm. Calculate the area of the trapezoid.

The Pythagorean theorem for the triangle AFC:

h2+(89+x)2=1202

h2=1202-(89+x)2

The Pythagorean theorem for the triangle EBD:

h2+(142-x)2=1532

h2=1532-(142-x)2

1202-(89+x)2=1532-142-x2

14400-7921+178x+x2=23409-20164-284x+x2

14400-7921-178x-x2=23409-20164+284x-x2

-178x-284x=23409-20164-14400+7921

-462x=-3234 |·-1

462x=3234 

x=3234 462

x=7

x+89+y=142

y=142-x-89

y=142-7-89

y=46

h2=1202-(89+x)2=1202-89+72=1202-962

h2=14400-6724=5184

h=5184

h=72

A=AAED+AEFCD+AFBC

AAED=x·h2

AAED=7·722

AAED=7·722=7·2·362=7·36

AAED=252

AEFCD=b·h=89·72

AEFCD=6408

AFBC=y·h2

AFBC=46·722=2·23·722=23·72

AFBC=1656

A=AAED+AEFCD+AFBC=252+6408+1656

A=8316