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What This Lesson Covers In this AP Calculus Unit 1 lesson, we explore the core concept that powers all of calculus — limits. When we write $$ \lim_{x \to a} f(x) = L $$ we are not asking for the value at $$ x=a $$. We’re studying how $f(x)$ behaves as $x$ gets arbitrarily close to $a$. The meaning of a limit (approach vs. arrival) Left-hand and right-hand limits Why some limits do not exist: jump, infinite, and oscillating discontinuities The link between infinite limits and vertical asymptotes Continuity and how it builds directly on limits Key Ideas at a Glance Approach, not plug-in: A limit can exist even if $f(a)$ is undefined. One-sided agreement: A limit exists at $x=a$ only if left-hand and right-hand limits are equal. Discontinuities: Jump: Left/right limits are finite but different. Infinite: Values grow without bound; signals a vertical asymptote. Oscillating: Values fail to settle to one number. Continuity at $x=a$: Requires all three: $f(a)$ is defined; $ \lim_{x\to a} f(x) $ exists; and $ \lim_{x\to a} f(x)=f(a) $. Why Limits Matter Limits are the language of change. They let us define instantaneous rates (derivatives) and accumulated change (integrals), even when direct substitution fails. Mastering limits makes every future AP Calculus topic more intuitive. Who This Video Is For Students preparing for AP Calculus AB/BC Learners who want a clear, concept-first introduction to calculus Anyone strengthening precalculus-to-calculus foundations Continue Learning with Us We’d love to hear from you! Whether you prefer email, WhatsApp, our website chat, WeChat, or Line, our team is ready to guide you personally. Reach out anytime! We’re here to make your learning smoother, faster, and more enjoyable. Quick Glossary Limit: The value $f(x)$ approaches as $x$ approaches a point. One-sided limits: Limits taken from the left ($x \to a^{-}$) or right ($x \to a^{+}$). Continuity: No breaks, jumps, or holes at a point; the limit equals the function value. Vertical asymptote: A vertical line $x=a$ where $f(x)$ grows without bound. Share & Subscribe If this helped, share it with a friend beginning calculus and subscribe for the upcoming lessons. See also AP Calculus AB Course Overview — College Board Khan Academy