Based on the needs of practical problems, the concept of square root is introduced to understand the meaning of square root, and the square root of some numbers will be found.

Emphasis and difficulty in teaching

Key point: Understand the concept of square root and find some non-negative square roots.

Difficulty: the meaning of square root.

teaching process

First, ask questions and create situations.

Question 1. What is the side length of a square piece of paper with an area of 25cm2?

Question 2. It is known that the area of a circle is 16πcm2 and the radius of the circle is long.

To solve these problems, learn this section.

Second, think about it:

1, can you solve the above two problems? What are the essence of these two questions?

Is the square root of 2 and 25 only 5? Why?

Does -4 have a square root? Why?

Third, knowledge introduction:

A positive number A has two square roots in opposite directions. We use a to represent the positive square root of a, which is pronounced as

"root number a", where a is called the square root. This root is called the arithmetic square root of A, and the other negative square root is marked as-A.00. The square root of 0 is 0, the arithmetic square root of 0 is also 0, and the negative number has no square root.

The operation of finding the square root of a number is called square root.

Four. Ability, knowledge and improvement

Students show their self-study results, and the teacher clicks.

1. The essence of two problems in the situation is to know the square of a certain number and find this number.

2. Summary: If the square of a number is equal to A, then this number is called the square root of A. 。

If 52 = 25, there are two square roots (-5) 2 = 25 ∴ 25: 5 and -5.

3. The square of any number is not equal to -4, so -4 has no square root.

Verb (abbreviation of verb) knowledge application

1, find the square root of the following number

①49② 1.69③(-0.2)2

2. Square the following figures.

① 1②0.09