Today we are going to:
• write algebraic expressions by
representing unknown
quantities; and
• evaluate algebraic expressions
by substituting the given value
for the variable.
Write an algebraic expression for
each of the following statements.
(a) Add 3 to p
p+3
(b) Subtract 2 from the product of 3
and x
3x – 2
(c) Divide the sum of
m+n
m and n by 5
5
(d) Multiply 7 to half of t
7t
2
Algebraic Expression in Two or more
unknown
Example :
State the number of unknown in each of the
following algebraic expressions.
(a) 2a + 2b (b) 100 – 2pqr (c) hjk + 8p – 19q
Answer :
• 2a + 2b has two unknown : a and b
• 100 – 2pqr has three unknown : p, q and r
• hjk + 8p – 19q has five unknown : h, j, k, p and q
Evaluating Algebraic Expression
*To evaluate an algebraic expression is to
find the value of the expression.
STEPS:
1. Substitute the given value for the variables
(replace letters with the given numbers)
2. Solve using the order of operations (PEMDAS)
Example :
Evaluate 2x + 5y when x = 4 and
y=2
Solution :
2x + 5y
= 2 (4) + 5 (2)
= 8 + 10
= 18
Evaluate p+2q+ 3r given p = 2
q = 4, r = 6
=2+ 2(4) + 3(6)
=2 + 8 + 18
=28
Example :
Evaluate 3c + 5 if c = 5 and d = 1
4d
Solution :
3c + 5 = 3 (5) + 5
4d
4 (1)
= 15 + 5
4
= 20
4
= 5
ALGEBRAIC EXPRESSIONS
Step 1 Substitute the given values
for the variables.
Step 2 Solve using the order of
Operations PEMDAS.
Problem 1
Given the formula
P=2L+2W, find the
value of P if K=7
and W=3.
Problem 2
If V=lwh, what is
the value of V when
l=2, w=3, and h=4?
Problem 3
If x=1 and y= -2, which
expression has a value of
3?
(a) x+y
(c) x-y
(b) xy
(d) y-x
Problem 4
If a=1 and b=-2,
find the value of
2
(a+b) .
Problem 5
Using the formula
2
V=x h, find V when
x=6 and h=2
Problem 6
Evaluate the
2
expression (6a) b if
a=2 and b=-1
Problem 7
Find the value of
3a-4b if a=-2 and
b=5.
Problem 8
Find the value of
2
(x -8x+4) if x=1/2.
Problem 9
2
5a -b
Evaluate
if
a=-2 and b=10.
Problem 10
Find the value of
3
the expression 3x
when x=-2
Problem 11
What is the value of
R=5 and S=-2.
2
RS
if
Problem 12
Evaluate the expression
2
3x +y if x=1 and y=-3.
Problem 13
Find the value of the
3
expression 2xy if x=3 and
y=-2
Problem 14
Find the value of
x=-3.
2
5x
if
Problem 15
If x=-3 and y=2, find the
2
value of (xy) .