22: division and the remainder theorem © christine crisp “teach a level maths” vol. 1: as core...
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22: Division and22: Division andThe Remainder The Remainder
TheoremTheorem
© Christine Crisp
““Teach A Level Maths”Teach A Level Maths”
Vol. 1: AS Core Vol. 1: AS Core ModulesModules
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Division and the Remainder Theorem
Module C1AQA Edexc
elOCR
MEI/OCR
Module C2
"Certain images and/or photos on this presentation are the copyrighted property of JupiterImages and are being used with permission under license. These images and/or photos may not be copied or downloaded without permission from JupiterImages"
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Division and the Remainder Theorem
We’ll first look at what happens when we divide numbers.
21327 e.g.
Quotient
2
13
2
7This can be written
as
Remainder
3 is called the quotient 1 is the remainder
Algebraic expressions can be divided in a similar way
Division
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Division and the Remainder Theorem
2
3 1
x
x 22
3 1
xx
x
2
1
xx
Quotient
Remainder
e.g. 1 Find the quotient and remainder when
is divided by
13 x
2x
Solution:
e.g. 2 Write in the form 3
3 532
x
xx 3x
CBxA
Solution: 33
3
3
3 532532
x
x
x
x
x
xx
3
532
x
x
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Division and the Remainder TheoremExercis
es Find the quotient and remainder when is divided by x
47 23 xx1.
xx
x
x
x 47 23
xxx
472
x
xx 47 23Solution:
Solution: 2
23 342
x
xxx 22
2
2
3 342
x
x
x
x
x
x
2
342
x
xx
The quotient is and the remainder is -4
xx 72
2. Write in the form 2x
DCxBAx
2
23 342
x
xxx
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Division and the Remainder Theorem
x2
Dividing by an expression of the form x - a can be done in 2 ways
Solution: Method 1 Long division.
• Divide the 1st term of the numerator by the 1st term of the denominator.
Write the division as follows:
e.g.1 Divide by62 x 1x
621 xxx 2
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Division and the Remainder Theorem
x2
621 xx
Write the division as follows:
• Write this answer above the polynomial being divided.
2
e.g.1 Divide by62 x 1x
Dividing by an expression of the form x - a can be done in 2 ways
Solution: Method 1 Long division.
x 2
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Division and the Remainder Theorem
621 xx
Write the division as follows: 2
e.g.1 Divide by62 x 1x
Dividing by an expression of the form x - a can be done in 2 ways
• Multiply x – 1 by this number . . . and write the answer
below• Subtract:6 – (– 2) = 8
8
The quotient is 2 and the remainder is 8.
So,1
82
1
62
xx
x
22 x
)1(2 x
22 x
Solution: Method 1 Long division.
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Division and the Remainder Theorem
1
x
)1( x
Dividing by an expression of the form x - a can be done in 2 ways
Solution: Method 2 ( Inspection )
e.g.1 Divide by62 x 1x
1
62
x
x• Write
• Copy the denominator onto the top line
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Division and the Remainder Theorem
1
x
Solution: Method 2 ( Inspection )
2 )1( xx2
• Divide the 1st term of the numerator . . .
Dividing by an expression of the form x - a can be done in 2 wayse.g.1 Divide by62 x 1x
• Write
• Multiply . . .
. . . by the 1st term of the denominator
x 21
62
x
x
so the 1st term at the top is now correct2x = 2x
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Division and the Remainder Theorem
1
x1
62
x
x 82 )1( x6
Dividing by an expression of the form x - a can be done in 2 wayse.g.1 Divide by62 x 1x
• Write
• Adjust the constant term . . .
2+ 6 =
1
8
1
)1(2
1
62
xx
x
x
x• Separate the 2 terms:
The quotient is 2 and the remainder is 8
+ 8
Solution: Method 2 ( Inspection )
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Division and the Remainder Theorem
Method 1 is very complicated for harder divisions, so from now on we
will use Method 2 only.
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Division and the Remainder Theorem
)1( x
Solution:
e.g.2 Divide by352 2 xx 1x
1
352 2
x
xx
1x
Write the denominator on the top line
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Division and the Remainder Theorem
1
352 2
x
xx )1( x22x
Solution:
e.g.2 Divide by352 2 xx 1x
1x
x2
Correct the 1st term.
22x 22x
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Division and the Remainder Theorem
1
352 2
x
xx )1( x )1( x
Solution:
e.g.2 Divide by352 2 xx 1x
1x
x2x5
x5 x2 x7
7
• Copy the denominator and correct the next term.
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Division and the Remainder Theorem
)1( x )1( x
Solution:
e.g.2 Divide by352 2 xx 1x
1
352 2
x
xx
1x
x2
• Correct the last term . . . 3 7 4
7 43
• Check the numerator.47722 2 xxx 352 2 xx
So,
1
352 2
x
xx1
472
xx
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Division and the Remainder Theorem
)1( x )1( x
Solution:
e.g.2 Divide by352 2 xx 1x
1
352 2
x
xx1x
x2
• Correct the last term . . .
7 4
• Check the numerator.
So,
1
352 2
x
xx1
472
xx
• Write the denominator on the top line
• Correct the 1st term.
• Copy the denominator and correct the next term.
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Division and the Remainder Theorem
)1( x
Solution:
e.g.3 Divide by32 23 xx 1x
1x
2x
33 xx
1
32 23
x
xx
Tip: As there is no linear x-term leave a space
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Division and the Remainder Theorem
)1( x )1( xx
Solution:
e.g.3 Divide by32 23 xx 1x
1x
2x
1
32 23
x
xx
2222 xxx
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Division and the Remainder Theorem
)1( x )1( x )1( x
Solution:
e.g.3 Divide by32 23 xx 1x
1x
2x
1
32 23
x
xx x 1
xx 0
xx )1(Be careful!
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Division and the Remainder Theorem
)1( x )1( x )1( x
Solution:
e.g.3 Divide by32 23 xx 1x
1x
2x
1
32 23
x
xx x
213
21
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Division and the Remainder Theorem
)1( x )1( x )1( x
Solution:
e.g.3 Divide by32 23 xx 1x
1x
2x
1
32 23
x
xx x 1 2
1
21
1
32 223
x
xxx
xx
The quotient is and the remainder is
212 xx
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Division and the Remainder Theorem
)2( x )2( x 8
Divide by x + 2442 xx1.
Solution:
The quotient is x + 2 and the remainder is
8
The solution is on the next slide
Exercises
2
442
x
xx
2x
2
82
x
x
2
442
x
xx
2. Divide by143 23 xxx 1x
x 2
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Division and the Remainder Theorem
)1( x )1( x )1( x
Solution:
1
143 23
x
xxx
1x
2x x2 6 7
1
762
1
143 223
x
xxx
xxx
The quotient is and the remainder is
7622 xx
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Division and the Remainder Theorem
e.g. Find the remainder when is
divided by x - 1
47 23 xx
The remainder theorem gives the remainder when a polynomial is divided by a linear factorIt doesn’t enable us to find the quotient
47)( 23 xxxfLet 4)1(7)1()1( 23 f
4
The method is the same as that for the factor theorem
The remainder is 4
The remainder theorem says that if we divide a polynomial by x – a, the remainder is given by
)(xf )(af
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Division and the Remainder Theorem
ax
Rxg
ax
xf
)(
)(
Proof of the Remainder theoremLet be a polynomial that is divided by x - a
)(xf
The quotient is another polynomial and the remainder is a constant.
We can write
Multiplying by x – a gives
Rxgaxxf )()()(
So, Ragaaaf )()()(
Raf )(
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Division and the Remainder Theorem
e.g.1 Find the remainder when is divided by
143 23 xxx2x
Solution: Let
143)( 23 xxxxf
1)2(4)2(3)2()2( 23 f
)2(2 fRa So,
18128 13 R
Tip: Use the remainder theorem to check the remainder when using long division. If the remainder is correct the quotient will be too!
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Division and the Remainder Theorem
e.g.2 Find the remainder when is divided by
4223 xxx12 x
Solution: Let
42)( 23 xxxxf
To find the value of a, we let 2x + 1 = 0. The value of x gives the value of a.
21012 xx
42212
213
21
21 f
4141
81
21 f
so, 21 fR
8
32821 R
8
21R
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Division and the Remainder Theorem
Exercises Find the remainder when is
divided by x + 1 534 23 xxx1.
Solution: Let
534)( 23 xxxxf
5R5341 R
5)1(3)1(4)1()1( 23 f
2. If x + 2 is a factor of and if the remainder on division by x – 1 is – 3, find the values of a and b.
623 bxaxx
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Division and the Remainder Theorem
Exercises
2. If x + 2 is a factor of and if the remainder on division by x – 1 is – 3, find the values of a and b.
623 bxaxx
06)2()2()2( 23 ba 0)2(f
3)1(f 361 ba
01424 ba
Solution: Let
6)( 23 bxaxxxf
2 ba - - - (2)
72 ba - - - (1)
(1) + (2)
393 aa
Substitute in (2)
1b
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Division and the Remainder Theorem
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Division and the Remainder Theorem
The following slides contain repeats of information on earlier slides, shown without colour, so that they can be printed and photocopied.For most purposes the slides can be printed as “Handouts” with up to 6 slides per sheet.
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Division and the Remainder Theorem
Dividing by an expression of the form x - a can be done in 2 ways:
Method 1: Long Division
Method 2: Inspection
Method 2 is usually easier but an example of method 1 is given next.
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Division and the Remainder Theorem
621 xx
Write the division as follows: 2
e.g.1 Divide by62 x 1x
• Multiply x – 1 by this number . . .
and write the answer below
• Subtract:6 – (– 2) = 8
8
The quotient is 2 and the remainder is 8.
So,1
82
1
62
xx
x
22 x)1(2 x
22 x
Solution: Method 1 Long division.
• Divide the 1st term of the numerator by the 1st term of the denominator.
• Write this answer above the polynomial being divided.
x2x 2
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Division and the Remainder Theorem
1
x1
62
x
x 82 )1( x6
e.g.1 Divide by62 x 1x
• Write
• Adjust the constant term
1
8
1
)1(2
1
62
xx
x
x
x• Separate the 2 terms:
The quotient is 2 and the remainder is 8
Solution: Method 2 ( Inspection )
• Copy the denominator onto the top line• Divide the 1st term of the numerator
• Multiply
by the 1st term of the denominator
so the 1st term at the top is now correct
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Division and the Remainder TheoremThe remainder theorem says that if we divide
a polynomial by x – a, the remainder is given by
)(xf )(af
ax
Rxg
ax
xf
)(
)(
Proof of the Remainder theoremLet be a polynomial that is divided by x - a
)(xf
The quotient is another polynomial and the remainder is a constant.
We can write
Multiplying by x – a gives
Rxgaxxf )()()(
So, Ragaaaf )()()(
R
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Division and the Remainder Theorem
Solution: Let
143)( 23 xxxxf
1)2(4)2(3)2()2( 23 f
)2(2 fRa So,
18128 13 R
Tip: Use the remainder theorem to check the remainder when using long division. If the remainder is correct the quotient will be too!
e.g.1 Find the remainder when is divided by
143 23 xxx2x
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Division and the Remainder Theorem
e.g.2 Find the remainder when is divided by
4223 xxx12 x
Solution: Let
42)( 23 xxxxf
To find the value of a, we let 2x + 1 = 0. The value of x gives the value of a.
21012 xx
42212
213
21
21 f
4141
81
21 f
so, 21 fR
8
32821 R
8
21R