English: That means nothing is going out, so that means the derivatives, so that is u_(x)(a,t) = 0, u_(x)(b,t) = 0.
Telugu: అంటే డెరివేటివ్‌లు అంటే u_(x)(a,t) = 0, u_(x)(b,t) = 0 గా ఉండాలి.