"Value of Algebraic Expressions" PPT Courseware 4

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"Value of Algebraic Expressions" PPT Courseware 4

Use matchsticks to build small fish as follows.

(1) How many matchsticks are used to catch n small fishes?

(2) How many matchsticks are needed to catch 20 such small fish?

What about 100 items?

The value of the algebraic expression:

According to the needs of the problem, use specific numerical values ​​to replace the letters in the algebraic expression. According to the operational relationships in the algebraic expression, the result obtained is the value of the algebraic expression.

Example 1. According to the following conditions, find the value of the algebraic expression 2a²-3ab+b².

(1) a= - 2 ,b= - 3; (2)a=-1 1/2 , b=4/3

Reflection and summary:

(1) Format: "When..."

(2) When substituting, the numbers should be substituted into the positions of the corresponding letters;

(3) When evaluating, the multiplication sign that was originally omitted must be added;

(4) If a negative number or fraction is substituted, brackets must be added.

(5) Generally speaking, when the value of letters in an algebraic expression changes, the value of the algebraic expression also changes accordingly.

Give it a try:

1. When x= - 2, find the value of the algebraic expression x²-2x-1.

2. When a=5,b=-2, find the value of the following algebraic expression:

(1)(a+2b)(a-2b) (2)a²-2b

3. Find the value of the algebraic expression according to the following conditions.

(1)x=-1/2 (2) x= - 2

Bring in the whole

(Question source) If a+b=-1, find the algebraic expression

(1)The value of a+b+2;

Solution: When a+b=-1, a+b+2=-1+2=1

(2)The value of 3a+3b.

Solution: When a+b=-1,

3a+3b=3(a+b)=3×(-1)=-3

Mathematics of life:

The weight of human blood accounts for about 6% of human body weight.

1. If a person weighs a kg, then how much does his blood weigh in kilograms?

2. Liangliang’s weight is 35kg. How many kilograms of blood volume is it?

3. Please estimate your blood weight.

Guess who is taller?

According to newspaper records, a doctor studied and found a formula for predicting the height of a child's adult height: a son's height is half the sum of his parents' heights, multiplied by 1.08. A daughter's height is 0.923 times the father's height plus the mother's height. and divided by 2.

(1) It is known that the height of the father is a meter and the height of the mother is b meters. Use algebraic expressions to express the heights of the son and daughter.

(2) The father of Xiaohong, a first-grade junior high school girl, is 1.75 meters tall, and her mother is 1.62 meters tall. The father of Xiaoming, a sixth-grade boy, is 1.70 meters tall, and her mother is 1.62 meters tall. Try to predict who will be taller, Xiaohong or Xiaoming, when they become adults. higher?

(3) Try to test your height as an adult.

Do it

When people meet, they shake hands to express friendship. Two people shake hands only once, and three people shake hands three times. How many times do four people shake hands when they meet?

Are there n people?

On Xiaoli's father's birthday, 10 old friends came over. If they wanted to shake hands with each other, how many times would they have to shake hands?

What did you learn today?

1. Steps to find the value of an algebraic expression: (1) Substitution, (2) Calculation;

2. Things to note when finding the value of an algebraic expression:

① When substituting, the letters should indicate the value "when..." and should be substituted into the corresponding position, but other operation symbols and original numbers remain unchanged.

② The multiplication sign that was originally omitted must be added when numbers are multiplied by numbers after substituting numbers.

③If the value of the letter is a fraction or a negative number, brackets should be added when substituting it.

3. The same algebraic expression can be regarded as a whole - whole substitution.

Pass the numbers game

Rules: Each study group selects four students to play a number-passing game.

The first classmate randomly reported a number to the second classmate.

The second student adds 1 to the number and passes it to the third student.

The third classmate then squared the number he heard and passed it to the fourth classmate.

Explanation point 1: Values ​​of algebraic expressions

This is a programming flow chart. Question: When x inputs 5, what is the final output result?

Generally speaking, using numerical values ​​to replace letters in an algebraic expression and calculating the result according to the operational relationships in the algebraic expression is called the value of the algebraic expression.

game rules

The first student multiplied the number he got by 2 and passed it to the second student. The second student added 3 to the number he got and passed it to the third student. The third student squared the number he got and passed it to the third student. The fourth student subtracted 5 from the result and passed it to the fifth student. The fifth student quickly wrote the result on the blackboard.

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For more information about the "Value of Algebraic Expressions" PPT courseware, please click on the "Value of Algebraic Expressions" ppt tag.

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Update Time: 2024-11-22

This template belongs to Mathematics courseware Hebei Education Edition Seventh Grade Mathematics Volume 1 industry PPT template

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