1.( 1) rectangle (2) diamond (3) square
2. Proof: In parallelogram ABCD. DC // AB
=
∴∠DCA=∠BAC.
And f are bisectors on AC.
∴AE=CF.
∴△DCF=S=△BAE(SAS)
∴DF=EB in the same way, DE=FB. A quadrilateral is a parallelogram.
3. Prove that ∵ quadrilateral ABCD is a parallelogram. ∴AB//CD。
=
And point EF are the midpoint of ABDC respectively. ∴EB//CF。
=
∴ Quadrilateral EBCF is a parallelogram.
∴EF=BC。
4. Proof: in RT△ABC and Rt△CDA.
∠B=∠D=90。 AB=CD。 AC=CA .
∴Rt△ABC=s= Rt△CDA (HL)
∴AD=BC .∴ quadrilateral ABCD valley parallelogram. ∫∠d = 90。 ∴ quadrilateral ABCD is a rectangle.
You know, group B 8.9.10.11.12, just tell me the answer.