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Unformatted text preview: on the homework. Problem 10.2.14: Find the points on the parametric curve x ( t ) = t + ln t, y ( t ) = t-ln t where the curve is concave up ( y > 0). Solution: dy dx = 1-1 t 1 + 1 t = t-1 t + 1 . So d dx dy dx = d dt t-1 t + 1 d dt ( t + ln t ) , which simplies to 2 t ( t + 1) 3 . Now we check signs of the numerator (changes from minus to plus at t = 0) and the denominator (changes from minus to plus at t =-1) to see that the curve is concave up at the points where t <-1 and where t > ....
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