curl --request POST \
  --url https://api.iotools.cloud/v1/tool/average-rate-of-change-calculator \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "functionExpr": "x^2",
  "a": "1",
  "b": "4"
}
'

{
  "tool": "average-rate-of-change-calculator",
  "tool_version": "1.0.2",
  "outputs": {
    "averageRateOfChange": "5",
    "secantLineEquation": "y = 5x - 4",
    "steps": "f(x) = x^2 on [1, 4]\nf(a) = f(1) = 1\nf(b) = f(4) = 16\nAverage rate of change: m = (f(b) − f(a)) / (b − a) = (16 − 1) / (4 − 1) = 5\nSecant line through (a, f(a)) and (b, f(b)): y − 1 = 5(x − 1)\n  y = 5x - 4"
  },
  "credits_used": 5,
  "credits_remaining": null
}