{
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   "cell_type":"markdown",
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   "source":[
    "<!-- jupyter-book 04_08_testdoc.ipynb -->\n",
    "# Exercise: Solution of differential equation\n",
    "\n",
    "<div id=\"sec:this:exer:de\"></div>\n",
    "\n",
    "\n",
    "\n",
    "\n",
    "**Question:** Given"
   ]
  },
  {
   "cell_type":"markdown",
   "metadata":{
    "editable":true
   },
   "source":[
    "$$\n",
    "\\frac{dy}{dx} = -y(x),\\quad y(0)=1\n",
    "$$"
   ]
  },
  {
   "cell_type":"markdown",
   "metadata":{
    "editable":true
   },
   "source":[
    "What is the solution of this equation?\n",
    "\n",
    "**Choice A:**\n",
    " $y=e^{-y}$\n",
    "\n",
    "**Choice B:**\n",
    " $y=e^{y}$\n",
    "\n",
    "**Choice C:**"
   ]
  },
  {
   "cell_type":"markdown",
   "metadata":{
    "editable":true
   },
   "source":[
    "from math import exp\n",
    "def f(x):\n",
    "    return exp(x)\n"
   ]
  },
  {
   "cell_type":"markdown",
   "metadata":{
    "editable":true
   },
   "source":[
    "**Choice D:**\n",
    " The solution cannot be found because there is a derivative in the equation.\n",
    "\n",
    "**Choice E:**\n",
    " The equation is meaningless: an equation must be an equation\n",
    "for $x$ or $y$, not a function $y(x)$."
   ]
  }
 ]
}