Chapter 1 - Section 1.7 - Introduction to Proofs - Exercises - Page 91: 20

See the solution.

$Proof.$ The consequent of $P(1)$ is $1^2\geq 1$. We know $1^2=1$, so the consequent of $P(1)$ is $1\geq 1$, which is true. Thus since $P(1)$ is a conditional sentence with a true consequent, $P(1)$ is true.$_\Box$ We proved $P(1)$ is true by showing its consequent is true. Therefore, we used a trivial proof.