Video narration
Keep forgetting the trig values for 0°, 30°, 45°, 60°, and 90°? You don't need five rows. Put one hand in front of you: from thumb to pinky, assign those angles in order-0°, 30°, 45°, 60°, 90°. Now number those finger positions 0 through 4, starting at the thumb. Here is the turn: sine follows one pattern, √n/2-the square root of n, divided by two. At each angle, use its position number n, take the square root, and divide by 2. That gives 0, 1/2, √2/2, √3/2, and 1. For cos, read the same numbers backward: use 4, 3, 2, 1, 0 instead. Tan is sin divided by cos, so use those two rows. At 90°, cos is zero, and division by zero is undefined, so tan 90° is undefined. For these standard first-quadrant angles, use your hand: forward for sin, backward for cos, divide for tan.