Science and Education Publishing American Journal of Mathematical Analysis 1 1 2013 11 03 Summability of a Jacobi Series by Lower Triangular Matrix Method 42 47 EN Binod Prasad Dhakal Tribhuvan University, Nepal AJMA2013134 10.12691/ajma-1-3-4 2013 10 13 2013 10 30 2013 11 03 The Jacobi polynomial P_n⁽α^,β⁾(x) which is obtained from Jacobi differential equation is an orthogonal polynomial over the interval [-1, 1] with respect to weight function _(1-x)α_(1+x)β, α>-1, β>-1. Here Jacobi series has been taken and established a theorem on lower triangular matrix summability of a Jacobi series.