小学平面图形公式大全：

长方形的周长=（长+宽）×2

正方形的周长=边长×4

长方形的面积=长×宽

正方形的面积=边长×边长

三角形的面积=底×高÷2

平行四边形的面积=底×高

梯形的面积=（上底+下底）×高÷2

直径=半径×2，半径=直径÷2

圆的周长=圆周率×直径= 圆周率×半径×2

圆的面积=圆周率×半径×半径

扇形的面积＝圆周率×半径²×（圆心角/360）

推荐阅读：
How To Protect Your Brand On Social Media　 Ways to Find Out if a Ghost Blogger is Right for You　 Why You SHOULDN’T Use WordPress as Your Blogging Platform　 How to Maximize Your Freelance Profits Using the Power of Emotio　 What to Expect from Hiring Outsourced Content Writers　 Call for Minimalism: How the New Wave of Blogging Platforms Give　 3 Easy Ways to Improve Writing Skills　 Explaining The Perfect Website Design to Non-Designers　 Clear Skies Ahead – The Shift to Cloud Computing　 Content Creation Versus Content Sharing