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Schaum's Outline of Theory and Problems of Beginning Calculus

Schaum's Outline of Theory and Problems of Beginning Calculus

Schaum's Outline of Theory and Problems of Beginning Calculus

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Chapter 20Most quantities encountered in science or in everyday life vary with time. If two such quantities arerelated by an equation, <strong>and</strong> if we know the rate at which one <strong>of</strong> them changes, then, by differentiatingthe equation with respect to time, we can find the rate at which the other quantity changes.EXAMPLES(a) A 6-foot man is running away from the base <strong>of</strong> a streetlight that is 15 feet high (see Fig. 20-1). If he moves atthe rate <strong>of</strong> 18 feet per second, how fast is the length <strong>of</strong> his shadow changing?Let x be the distance <strong>of</strong> the man from the base A <strong>of</strong> the streetlight, <strong>and</strong> let y be the length <strong>of</strong> the man'sshadow.GEOMETRY Two triangles,Xare similar if their angles are equal in pairs: 3c A = %X, 3c B = % Y, % C = 3cZ. (For this condition to hold,it suffices that two angles <strong>of</strong> the one triangle be equal to two angles <strong>of</strong> the other.) Similar triangles havecorresponding sides in fixed ratio :147

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