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A parallelogram containing a 60^0 angle ...

A parallelogram containing a `60^0` angle has perimeter `p` and its longer diagonal is of length `ddot` Find its area.

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Perimeter=`2(x+y)=P`
`x+y=P/2-(1)`
`In/_ABD`
`d^2=y^2sin^2 60+(x+ycos60)^2`
`d^2=y^2sin^2 60+x^2+y^2cos^2 60+2xycos60`
`d^2=x^2+y^2+2xy*1/2`
`d^2=x^2+y^2+xy`
`d^2=(x+y)^2-xy`
...
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