The ASTC Rule is a mnemonic device used to remember the signs of trigonometric functions in each of the four quadrants of the Cartesian coordinate system. It stands for 'All Students Take Calculus,' indicating that in the first quadrant, all trigonometric functions are positive, in the second quadrant only sine and its reciprocal function cosecant are positive, in the third quadrant only tangent and its reciprocal function cotangent are positive, and in the fourth quadrant only cosine and its reciprocal function secant are positive.
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