Learning goals: Teacher Facing Comprehend the term “irrational number” (in spoken language) to mean a number that is not rational and that $\sqrt{2}$ is an example of an irrational number. Comprehend the term “rational number” (in written and spoken language) to mean a fraction or its opposite. Determine whether a given rational number is a solution to the equation $x^2=2$ and explain (orally) the reasoning. Full lesson plan (warm-up, activities, synthesis, cool-down prompt) from 8.8 Pythagorean Theorem and Irrational Numbers, Grade 8.