1. Binomial Theorem Introduction
L.O.
all pupils can describe a binomial expression
all pupils recognise the relationship between the Binomial Expansion and Pascal's Triangle
all pupils understand how to use the Binomial Theorem to expand Binomial expressions

2. describe a binomial expression Starter:
Binomial Expansion and Pascal's Triangle

3. Starter ? ? ? ? ? ? ? Expand (a + b)0 Expand (a + b)1 Expand (a + b)2
1a ab b2
1a a2b ab b3
1a a3b a2b ab b4 ? ? ? ? ?
What do you notice about: ?
The coefficients: They follow Pascal’s triangle.
The powers of a and b: Power of a decreases each time (starting at the power)
Power of b increases each time (starting at 0) ?

4. Quickfire Pascal
What coefficients in your expansion do you use if the power is: 2: ?

5. Quickfire Pascal
What coefficients in your expansion do you use if the power is: 4: ?

6. Quickfire Pascal
What coefficients in your expansion do you use if the power is: 3: ?

7. Quickfire Pascal
What coefficients in your expansion do you use if the power is: 5: ?

8. Quickfire Pascal
What coefficients in your expansion do you use if the power is: 2: ?

9. Quickfire Pascal
What coefficients in your expansion do you use if the power is: 4: ?

10. Quickfire Pascal
What coefficients in your expansion do you use if the power is: 3: ?

11. Quickfire Pascal
What coefficients in your expansion do you use if the power is: 5: ?

12. Quickfire Pascal
What coefficients in your expansion do you use if the power is: 4: ?

13. Binomial Expansion 1 4 6 4 1 (2y) (2y)2 (2y)3 (2y)4
(x + 2y)4 =
x x x x
(2y) (2y) (2y) (2y)4
= x4 + 8x3y + 24x2y2 + 32xy3 + 16y4
Step 1: You could first put in the first term with decreasing powers.
Step 2: Put in your second term with increasing powers, starting from 0
(i.e. so that 2y doesn’t appear in the first term of the expansion, because the power is 0)
Step 3: Add the coefficients according to Pascal’s Triangle.

14. = (2x)3 + 3(2x)2(-5) + 3(2x)(-5)2 + (-5)3 = 8x3 – 60x2 + 150x – 125
Your go... ? ?
(2x – 5)3
= (2x)3 + 3(2x)2(-5) + 3(2x)(-5)2 + (-5)3
= 8x3 – 60x x – 125
Bro Tip: If one of the terms in the bracket is negative, the terms in the result will oscillate between positive and negative.
The coefficient of x2 in the expansion of (2 – cx)3 is 294.
Find the possible value(s) of the constant c.
(2 – cx)3 = (-cx) (-cx)
So coefficient of x2 is 6c2 = 294
c =  7
Bro Tip: When asked about a particular term, it’s helpful to write out the first few terms of the expansion, until you write up to the one needed. There’s no point of simplifying the whole expansion!

15. Binomial Theorem Introduction
L.O.
all pupils can describe a binomial expression
all pupils recognise the relationship between the Binomial Expansion and Pascal's Triangle
all pupils understand how to use the Binomial Theorem to expand Binomial expressions

16. But what actually is the Binomial Expansion?

17. 1

18. Binomial Coefficients
This is known as a binomial coefficient. It can also be written as nCr
(said: “n choose r”) ? ? ? ? ? ? ? ?

19. Binomial Coefficients
To calculate Binomial Coefficients easily:
Because when we divide 8! by 6!, we cancel out all the numbers between 1 and 6 in the product.
i.e. The bottom number of the binomial coefficient (2) tells us how many consecutive numbers we multiply together. ? ? ? ? ?

20. General formula
Edexcel May 2013 (Retracted) ?

21. Using Binomial Expansions for approximations
Edexcel Jan 2012 ?
If , then x = 0.1. Plugging this in to our expansion: =
Actual value is (1.025)8 = So it is correct to 4dp!

22. Using Binomial Expansions for approximations
Exercise 5C Q7
Write down the first four terms in the expansion of
By substituting an appropriate value for x, find an approximate value to (0.99)6. Use your calculator to determine the degree of accuracy of your approximation.
1 – 0.6x x2 – 0.02x3
, which is accurate to 5dp ? Q8
Write down the first four terms in the expansion of
By substituting an appropriate value of x, find an approximate value to (2.1)10. Use your calculator to determine your approximation’s degree of accuracy.
x x x3
, which is accurate to 3sf ?

23. Using Binomial Expansions for approximations
Edexcel January 2007
1 + 5(-2x) + 10(-2x)2 + 10(-2x)3 = 1 – 10x + 40x2 – 80x3
We discard the x2 and x3 terms above. (1+x)(1-10x) = 1 – 10x + x – 10x2 = 1 – 9x – 10x2  1- 9x (since we can discard the x2 term again) ? ?