Desmos

Graphing calculator.
Features:
Graphing: Plot polar, Cartesian, or parametric graphs. There’s no limit to how many expressions you can graph at one time - and you don’t even need to enter expressions in y= form!
Sliders: Adjust values interactively to build intuition, or animate any parameter to visualize its effect on the graph
Tables: Input and plot data, or create an input-output table for any function
Statistics: Find best-fit lines, parabolas, and more.
Zooming: Scale the axes independently or at the same time with the pinch of two fingers, or edit the window size manually to get the perfect window.
Points of Interest: Touch a curve to show maximums, minimums, and points of intersection. Tap the grey points of interest to see their coordinates. Hold and drag along a curve to see the coordinates change under your finger.