ForHosting KIT · Developer Utilities

Concave up intervals calculator

A twice-differentiable graph is concave up on an open interval when its second derivative is strictly positive there: the slope is increasing and the curve bends like a cup that can hold water.

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

For a univariate polynomial given by a coefficient list, the second derivative is another polynomial that can be built with the power rule alone and analysed with a classical sign chart—no graphing calculator, no computer-algebra subscription, and no floating-point black box that disagrees with hand factoring. This concave up intervals calculator accepts coefficients highest degree first, forms p prime and p double prime, finds every distinct real root of the second derivative, tests the open pieces of the real line between those roots, and returns the open intervals where p double prime stays positive, together with readable polynomial strings for classroom display. Homework checks, tutoring platforms, exam generators, and light engineering notebooks all need the same deterministic answer for the same coefficients; the free browser widget and the prepaid API share one pure module so goldens and production scripts never disagree on whether a cubic is concave up on half the line or nowhere.

How to use it

Enter your values in the form above. The tool checks them before calculating and shows the result on the same page.

Check your inputs

Use the labels and units shown next to each field. If something is missing or outside the allowed range, the page points to the field to fix.

Use it again or automate it

Use the browser tool for individual checks and the API when you need the same capability in an automated workflow.

What you can do with it

Get an answer now

Enter one set of values and see the result without building a spreadsheet or script.

Compare scenarios

Change one value at a time and rerun the calculation to understand what affects the result.

Automate repeated work

Use the API when the same calculation needs to run inside your product or workflow.

FAQ

How do I use this capability?

Complete the fields above and run it on this page. The form highlights anything that needs attention.

For developers — API access

Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.

API endpoint

POSThttps://api.kit.forhosting.com/calculus/concave-up-intervals

Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.

Call it from your stack

curl -X POST https://api.kit.forhosting.com/calculus/concave-up-intervals \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"coefficients":[1,0,-3,0]}'

const res = await fetch("https://api.kit.forhosting.com/calculus/concave-up-intervals", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "coefficients": [
      1,
      0,
      -3,
      0
    ]
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/calculus/concave-up-intervals",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "coefficients": [
        1,
        0,
        -3,
        0
    ]
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/calculus/concave-up-intervals", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"coefficients":[1,0,-3,0]}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"coefficients":[1,0,-3,0]}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/calculus/concave-up-intervals", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "coefficients": [
    1,
    0,
    -3,
    0
  ]
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "calculus.concave_up_intervals",
  "status": "queued",
  "_links": {
    "result": "/tasks/tsk_…/result"
  }
}

The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.

Pricing

Per request$0.002

Published price — no tokens, no invented credits. A failed task is never charged.

Errors

HTTP	Code	Meaning
`401`	`unauthorized`	Missing or invalid API key.
`402`	`insufficient_balance`	Your balance doesn't cover the task price.
`404`	`unknown_type`	That task type doesn't exist.
`429`	`rate_limited`	Too many requests. Use the webhook instead of polling.

Read the full KIT documentation →