Solutions and stability of generalized Kannappan's and Van Vleck's functional equations

Elqorachi Elhoucien, Redouani Ahmed

We study the solutions of the integral Kannappan's and Van Vleck's functional equations $${\int }_{S}f(xyt)d\mu (t)+{\int }_{S}f(x\sigma (y)t)d\mu (t)=2f(x)f(y),x,y\in S;$$ $$\int_{S}f( xσ(y)t)…