    1. Chapter 6 Class 12 Application of Derivatives
2. Serial order wise
3. Examples

Transcript

Example 41 An Apache helicopter of enemy is flying along the curve given by = 2 + 7. A soldier, placed at (3, 7), wants to shoot down the helicopter when it is nearest to him. Find the nearest distance. The curve is given as y = x2 + 7 Let helicopter be at point (x, y) = (x, x2 + 7) Let d be the distance between helicopter soldier at (3, 7) d = 2 1 2+ 2 1 2 d = 3 2+ ( 2 +7) 7 2 d = 3 2+ 4 We need to find nearest distance i.e. minimum value of d Let f(x) = d2 f(x) = (x 3)2 + x4 When f(x) is minimum, d is minimum Finding f (x) f (x) = 2(x 3) + 4x3 = 2x 6 + 4x3 = 4x3 2x 6 Factorizing f (x) f (1) = 4(1)3 2(1) 6 = 4 + 2 6 = 0 Hence, (x 1) is a factor of 4x3 2x 6 Thus, f (x) = (x 1) (4x2 + 4x + 6) Hence f (x) = 0 gives Hence there is only one point x = 1 This is either the maxima or minima. Hence we find f (x) f (x) = (4x3 + 2x 6) f (x) = 12x2 + 2 Finding value at x = 1,. f (1) = 12(1)2 + 2 = 12 + 2 = 14 Since f (x) > 0 x = 1 is the minima. The value of f(1) is f(1) = (1 3)2 + 14 = ( 2)2 + 1 = 4 + 1 = 5 Hence, minimum distance between soldier & Helicopter d = (1) d =

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