We say that a boolean circuit is boring if it returns the same  result for $>\frac34$ possible input, where we have $n$ input gates.  Hence, boring circuit returns the same output ($0$ or $1$) for  $>\frac34 2^n$ inputs.   Prove that checking if boolean circuit is boring is NP-completeCan you help me? I have no idea how to start. I tried to reduce $3$-SAT but no result. 
Show that boring boolean circuit belongs to NP-complete class
complexity theory;np complete;circuits
Given a Boolean formula $\varphi$, let $x,y$ be two fresh variables, and consider the circuit computing the function$$x \lor y \lor \varphi.$$This circuit is boring iff $\varphi$ is satisfiable.