The circuit is equivalent to

The gate circuit can be shown by giving two inputs A and B$. <img src="https://cdn-question-pool.Quantrex.app/pyq/neet/GpMTblak0gWCdQq5W1ilca-1wyV6n4a84gwrV2I8C-A.original.fullsize.png"> Output of NOR gate,$Y_1=\overline{A+B}Output of $NAND gate,$$\begin{aligned} Y_2 & =\overline{Y_1 \cdot Y_1} \\ & =\overline{\overline{A+B} \cdot \overline{A+B}} \\ & =\overline{\overline{A+B}}+\overline{\overline{A+B}} \\ & =(A+B)+(A+B) \\ & =A+B \end{aligned}$$$Output of NOT gate,$$\begin{aligned} Y & =\overline{Y_2} \\ & =\overline{A+B} \end{aligned}which is$ the output of NOR gate. Altemative :<img src="https://cdn-question-pool.Quantrex.app/pyq/neet/kRL6QRuOKwEQhxGzDw0CcF_JeFt2RJcqaudiYUYEV0w.original.fullsize.png"> <img src="https://cdn-question-pool.Quantrex.app/pyq/neet/5GvRzpHYfCA9BRDrTOz_cCHW2AA0SbcQlr6LwVyzWyc.original.fullsize.png"> Same as NOR Gate NOR Gate\begin{array}{lll}0 & 0 & 1 \\ 0 & 1 & 0 \\ 1 & 0 & 0 \\ 1 & 1 & 0\end{array}$$Note : NOR and NAND gates are said to be universal building blocks.$