The dynamics of leaf area accorded with the curves of second-order equation.
叶面积消长动态符合一元二次方程变化曲线；
It's a second-order equation in x, and is a parabola and a parabola has this shape.
这是一个x的二次方程，也是一个抛物线方程式,抛物线都长这样。
By using a fixed point theorem in cones, we investigate a second-order equation and the theorem of existence of unique positive periodic solution is given.
应用不动点定理，研究了一类二阶时滞微分方程，给出了其唯一周期正解的存在性定理。
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