Let there be two goods 1 and 2. Let x₁ and x₂ denote their respective quantities. (x₁,x₂) represents a bundle. Suppose a consumer's preference over bundles in R₊^z can be represented by the utility function U(x₁,x₂) = min(x₁,2x₂). Prove that the consumer's preferences over bundles in R₊^z are convex by proving that the utility function is quasiconcave in R₊^z.