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If y = (3x – 4)/(x+2) then what s the value of dy/dx?(a) dy/dx(b) y(c) 1/ (dy/dx)(d) A constantThe question was posed to me during an online exam.Enquiry is from First Order Derivative in division Limits and Derivatives of Mathematics – Class 11 |
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Answer» CORRECT OPTION is (c) 1/ (dy/dx) To explain: It is given that y = (3x – 4)/(x + 2) ……….(1) Now differentiating both the sides, we get that, dy/dx = (x + 2)*3 – (3x – 4)/(x + 2)^2 = 10/(x + 2)^2 Again from (1) we get, xy + 2y = 3x – 4 or, x = – 2(y + 2) Thus dx/dy = -2* ((y – 3) – (y + 2))/ (y – 3)^2 Or, y – 3 = (3x – 4)/(x + 2) – 3 = -10/(x + 2) Thus, dx/dy = 10/(-10/(x + 2))^2 = (x + 2)2/10, where,x ≠ 0 i.e. dx/dy ≠ 0 Therefore, dy/dx*dx/dy = 10/(x + 2)2 * -10/(x + 2) = 1 => dy/dx = 1/(dy/dx) |
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