x=0
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Just as the slope of the tangent line to the graph of f at the point (x, f(x)) describes the behavior of the function, concavity describes the behavior of the slope. As x increases (graph goes from left to right), one of the following is true:Concavity is positive, so the slope slowly increases.Concavity is negative, so the slope slowly decreases.Concavity is equal to zero, so the slope is constant.Again, remember that concavity directly affects the slope, NOT the function itself. I mean this in the sense that concavity affects slope affects function.Mathematically speaking, you can find the concavity at a certain point by taking the derivative of the derivative of the function (accurately called the second derivative, f''). So, when you take the derivative of a function, you get the first derivative, f' (describing slope), and the derivative of that is the second derivative (describing the concavity).Last but not least, here is a handy way to find the concavity of a function by looking at its graph:Concavity is positive when the graph turns up, like a smiling emoticon (look at a graph of f(x) = x2 for an example).First observe that f'(x) = 2x.We see that f' < 0 when x < 0 and f' > 0 when x > 0. So that the graph is decreasing on the negative real axis and the graph is increasing on the positive real axis.Next observe that f''(x) = 2.Thus, f'' > 0 at all points. Thus the graph is concave up everywhere.Finally observe that the graph passes through the origin.Concavity is negative when the graph turns down, like a frowning emoticon (look at a graph of f(x) = -x2 for an example).First observe that f'(x) = -2x.We see that f' > 0 when x < 0 and f' < 0 when x > 0. So that the graph is increasing on the negative real axis and the graph is decreasing on the positive real axis.Next observe that f''(x) = -2.Thus, f'' < 0 at all points. Thus the graph is concave down everywhere.Finally observe that the graph passes through the origin.Look at the graph of f(x) = x3First observe that f'(x) = 3x2.Thus, f' ≥ 0 everywhere. The function is always increasing.Next observe that f''(x) = 6x.Thus, f'' < 0 when x < 0 and f'' > 0 when x > 0. So the graph is concave down on the negative real axis and concave up on the positive real axis.Finally observe that the graph passes through the origin.Concavity is zero when the graph is linear OR at a point where it stops turning up and starts turning down, and vice versa.
The graph of y = log(x) is defined only for x>0. The graph is a monotonic increasing function over its domain. It starts from an asymptotic "minus infinity" when x approaches 0. It passes through the value y = 0 when x = 1. The graph is illustrated at the link below.
the graph of cos(x)=1 when x=0the graph of sin(x)=0 when x=0.But that only tells part of the story. The two graphs are out of sync by pi/2 radians (or 90°; also referred to as 1/4 wavelength or 1/4 cycle). One cycle is 2*pi radians (the distance for the graph to get back where it started and repeat itself.The cosine graph is 'ahead' (leads) of the sine graph by 1/4 cycle. Or you can say that the sine graph lags the cosine graph by 1/4 cycle.