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 April 8th, 2014, 01:52 AM #1 Member   Joined: Sep 2013 Posts: 75 Thanks: 0 finding values of cubic function f(x) =ax^3 + cx - 2. The graph cuts x-axis @ (-1;0) and A(2;0). Show by calculation tha a = 1 and c = -3. This is how I tried the problem. f(-) = 0. And f(2) =0. a(-1)^3 + c(-1) -2 = 0. -a - c = 2. ...........(1) a(2)^3 + c(2) - 2 = 0. 8a +2c = 2 ........(2). but my answer book says equation (1) is -a+c = 3. and equation (2) is 8a -2c =2. where did I lost it? April 8th, 2014, 02:00 AM #2 Senior Member   Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,211 Thanks: 522 Math Focus: Calculus/ODEs Looks to me like you did well, and the equations given by your book are wrong. April 8th, 2014, 07:30 AM #3 Member   Joined: Sep 2013 Posts: 75 Thanks: 0 So I have. -a - c = 2 ......(1). 8a + 2c = 2.......(2). Now multiply (1) by 2 and add the two. -2a -2c = 4. Adding. 8a +(-2a) +2c +(-2c) =2+4. 6a= 6. a=1. 8(1) + 2c = 2. 6 = -2c. c =-3 April 8th, 2014, 07:31 AM #4 Member   Joined: Sep 2013 Posts: 75 Thanks: 0 I gt it Tags cubic, finding, function, values ### cubic function show by calculation that a=1 and c=-3

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