Аннотация:The first observation of the $$ {B}_c^{+}\to J/\psi {\pi}^{+}{\pi}^0 $$decay is reported with high significance using proton-proton collision data, corresponding to an integrated luminosity of 9 fb−1, collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV. The ratio of its branching fraction relative to the $$ {B}_c^{+}\to J/\psi {\pi}^{+} $$channel is measured to beBBc+→J/ψπ+π0BBc+→J/ψπ+=2.80±0.15±0.11±0.16,$$ \frac{{\mathcal{B}}_{B_c^{+}\to J/\psi {\pi}^{+}{\pi}^0}}{{\mathcal{B}}_{B_c^{+}\to J/\psi {\pi}^{+}}}=2.80\pm 0.15\pm 0.11\pm 0.16, $$