DETERMINING THE NUMBER OF SOLUTIONS

About "Determining the number of solutions"

Determining the number of solutions :

When we solve a linear equation in one variable, we may find exactly one value of x that will make the equation a true statement. But, when we simplify some equations, we may find that they have more than one solution or they do not have solution.

The table given below explains the situations where we have exactly one solution, more than one solution and infinitely many solutions for a linear equation in one variable.

Determining the number of solutions - Examples

Example 1 :

Use the properties of equality to simplify the equation given below. Say whether the equation has one, zero, or infinitely many solutions.

4x - 3  =  2x + 13

Solution :

Solve the given equation.

Step 1 :

Add 3 to both sides.

aaaaaaaaaaaaaaaaa 4x - 3  =  2x + 13 aaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaa      + 3           +  3 aaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaa ------------------- aaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaa 4x        =  2x + 16 aaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaa ------------------- aaaaaaaaaaaaaaaaaa

Step 2 :

Subtract 2x from both sides.

aaaaaaaaaaaaaaaaa 4x        =  2x + 16 aaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaa  - 2x          - 2x aaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaa ---------------------- aaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaa     2x        =         16 aaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaa ---------------------- aaaaaaaaaaaaaaaaaa

Step 3 :

Divide both sides by 2.

2x / 2  =  16 / 2

x  =  8

Justify and evaluate :

Plug x = 8 in the given equation.

4(8) - 3  =  2(8) + 13  ?

32 - 3  =  16 + 13  ?

29  =  29 ------> True

Plug some other value for x, say x  =  10.

4(10) - 3  =  2(10) + 13  ?

40 - 3  =  20 + 13  ?

37  =  23  False

Only x = 8 makes the equation a true statement and not any other value. So, there is only one solution, that is x = 8.  a

Example 2 :

Use the properties of equality to simplify the equation given below. Say whether the equation has one, zero, or infinitely many solutions.

4x - 5  =  2(2x - 1) - 3

Solution :

Solve the given equation.

Step 1 :

Use distributive property.

4x - 5  =  2(2x) - 2(1) - 3

Simplify

4x - 5  =  4x - 2 - 3

4x - 5  =  4x - 5

Step 2 :

We find the same coefficient for x on both sides.

So, subtract 4x on both sides to get rid of x-terms.

aaaaaaaaaaaaaaaaa 4x - 5  =  4x - 5 aaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaa  - 4x         - 4x    aaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaa  -------------------- aaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaa      - 5   =      - 5 aaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaa  --------------------- aaaaaaaaaaaaaaaaaa

When we solve the given equation, we don't find "x" in the result. But the statement (-5 = -5) we get at last is true. So there are infinitely many solutions.

Example 3 :

Use the properties of equality to simplify the equation given below. Say whether the equation has one, zero, or infinitely many solutions.

4x + 2  =  4x - 5

Solution :

Solve the given equation.

We find the same coefficient for x on both sides.

So, subtract 4x on both sides to get rid of x-terms.

aaaaaaaaaaaaaaaaa 4x + 2  =  4x - 5 aaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaa  - 4x         - 4x    aaaaaaaaaaaaaaaaaaaa  aaaaaaaaaaaaaaa  -------------------- aaaaaaaaaaaaaaaaaa   aaaaaaaaaaaaaaaaa        2  =      - 5 aaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaa  --------------------- aaaaaaaaaaaaaaaaaa

When we solve the given equation, we don't find "x" in the result. But the statement (2 = -5) we get at last is false. So there is no solution.

After having gone through the stuff given above, we hope that the students would have understood "Determining the number of solutions".

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