1.

A quadrilateral ABCD is drawn to circumscribe a circle. Prove that AB+CD=AD+BC. or A circle touches all the four sides of a quadrilateral ABCD. Prove that AB+CD=BC+DA.

Answer»

SOLUTION :LET the circle touches the sides AB,BC,CD and DA of a SQUAREABCD at P,Q,R and S respectively. Since, the tangents drawn from an external point to a circle are equal in length.
`:.""AP=AS""...(1)`
`BP=BQ""...(2)`
`CR=CQ""...(3)`
and`""DR=DS""...(4)`
Adding (1), (2), (3) and (4), we get
`ubrace(AP+BP)+ubrace(CR+DR)=AS+BQ+CQ+DS`
`implies""AB+CD=(AS+DS)+(BQ+CQ)`
`implies""AB+CD=AD+BC""` Hence Proved.


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