The document discusses rational expressions in mathematics for grade 8, emphasizing the evaluation of expressions by replacing variables with given values. It outlines that a rational expression is undefined when its denominator equals zero and provides examples of evaluating various rational expressions. Additionally, it instructs on finding values that will make certain expressions undefined.

1. Rational
Expressions
Grade 8 | Mathematics

2. Evaluate x-3, 2x+1, and
using the given values.
x-3
2x+1
x x-3 2x+1
0
2
50
1 000
10 000
100 000
x-3
2x+1

3. • A rational expression in one variable is
an expression that can be written in the
form where P and Q are polynomials
in one variable and Q ≠ 0
Rational Expressions
P
Q

4. written in the form where P and Q are
polynomials and Q ≠ 0
Rational Expressions
P
Q
Examples 4
x–2
4x
x2 – 9
x – 8
6x2
x2 + 2x – 35
3x + 4

5. x2 – 3
x – 2
If x = 0
02 – 3
0 – 2
-3
-2
= =
In evaluating algebraic expressions,
we replace the variables with the given
values and then simplify the resulting expression
3
2

6. x2 – 3
x – 2
If x = 1
12 – 3
1 – 2
-2
-1
= =
In evaluating algebraic expressions,
we replace the variables with the given
values and then simplify the resulting expression
2

7. 2a2
a – 3
Find the value of a to make
the expression undefined
A rational expression is undefined only
if its denominator is zero (0).

8. 7
(x–2) (x+1)
Find the value of x to make
the expression undefined
A rational expression is undefined only
if its denominator is zero (0).

9. 3a + 4b
a–b
Find the value of a and b to
make the expression undefined
A rational expression is undefined only
if its denominator is zero (0).

10. 1
2
3
4
5
6
8
9
10
7
11
12
13
17
18
20
16
19
14

11. Evaluate the rational
expression if x = 4 and y = 101
5x2
8y

12. 1 Evaluate the rational
expression if x = 0 and y = 11
5x2
8y
2

13. Evaluate the rational
expression if a = 3 and b = 6
a
b2
13

14. 1
c – 4
2d
Evaluate the rational
expression if c = 4 and d = 24

15. 1 Evaluate the rational
expression if e = -6 and f = 5
3e
4 – f2
5

16. Evaluate the rational
expression if g=-2 and h=2
g + 6
2h – 3
16

17. 3x
x – 2
1 Evaluate the rational
expression if g=-2 and h=27

18. 1
a
b2
Evaluate the rational
expression if a=-5 and b=108

19. 1 Evaluate the rational
expression if c=10and d=69
c – 4
2d

20. 1 Evaluate the rational
expression if e = 8 and f = 210
3e
4 – f2

21. 1
a
b2
Find the value of a to make
the expression undefined11

22. 1
a
b2
Find the value of a to make
the expression undefined12

23. 1 Evaluate the rational
expression if a=3 and b=6
a
b2
Find the value of a to make
the expression undefined13

24. 1 Evaluate the rational
expression if a=3 and b=6
a
b2
Find the value of a to make
the expression undefined14

25. 1 Evaluate the rational
expression if a=3 and b=6
a
b2
Find the value of a to make
the expression undefined15

26. 1 Evaluate the rational
expression if a=3 and b=6
a
b2
Find the value of a to make
the expression undefined16

27. 1 Evaluate the rational
expression if a=3 and b=6
a
b2
Find the value of a to make
the expression undefined17

28. 1 Evaluate the rational
expression if a=3 and b=6
a
b2
Find the value of a to make
the expression undefined18

29. 1 Evaluate the rational
expression if a=3 and b=6
a
b2
Find the value of a to make
the expression undefined19

30. 1 Evaluate the rational
expression if a=3 and b=6
a
b2
Find the value of a to make
the expression undefined20