φ ( λ 1 x 1 + λ 2 x 2 + ⋯ + λ n x n ) ≤ λ 1 φ ( x 1 ) + λ 2 φ ( x 2 ) + ⋯ + λ n φ ( x n ) \varphi(\lambda_1 x_1+\lambda_2 x_2+\cdots+\lambda_n x_n)\leq \lambda_1 \varphi(x_1)+\lambda_2\,\varphi(x_2)+\cdots+\lambda_n \varphi(x_n)