4 Strategies To Solve A Binomial Proof

Posted on September 8, 2017 by Matrix Education

Often binomial proofs can be the most difficult questions in the Maths Extension 1 exam, with students struggling to approach these complex proofs. However, there are certain strategies that you can use to tackle these questions. Your first step is to expand maths1 , or a similar expression if otherwise stated in the question.

binomial proofs 1

Your next step is to consider the four strategies below.


1. Substitution

When to use it: Examine the final term in your expansion and see if replacing  with a number will make your expansion look like the answer. However, if you are unsure then it is fine to use trial and error. This won’t take too long as the only substitutions I’ve only ever seen required are x= -1, -1, 0, 1 or 2. Consider the example below.

Question 1:

Use the expansion maths1 to prove bin1 has a value of 1 when n is even and a value of -1 when n is odd.

2. Differentiation

When to use it: Look for signs of differentiation in the answer, most notably anything to the power of (n-1), such as n2n-1. This indicates that you must differentiate both sides of your expanded equation. Very often after differentiating, you need to make a substitution for x. Note that some questions may require you to differentiate twice.

Question 2:

Use the expansion maths1 to prove that

bin2

3. Integration

When to use it: Look for signs of integration. Something raised to the power of (n + 1) in the answer is a clear sign. When integrating, consider using a definite integral; the limits are often easy numbers such as x = 0, ±1, or ±2. Note that you may be required to integrate twice. In this situation, integrate without limits, which will result in a +C . You can easily find out this constant by substituting x= 0 into both sides of the equation. Once C is found, you can then integrate again if required.

Question 3:

Use the expansion maths1 to prove

bin4
 

4. Expanding the binomial in 2 different ways

This method involves rewriting a binomial expression in a different way, such as bin5 followed by equating coefficients of a specific term, such as x2.

When to use this method: First, it is important to understand what bin9 means in terms of coefficients.bin9 is the coefficient of xin the expansion of bin7 is the coefficient of x6 in the expansion of bin8 etc.

With this in mind we can recognize that we must expand the binomial in the question in 2 ways when the power of the expansions differ. For example, if the question is to prove bin6, then you must consider the expansion binomial10 and then equate coefficients of like terms.

Question 4: 

Use the expansion of bin11 to show

bin12
With these techniques in mind, the next step is to practise! Examiners can be very creative in how they present these types of questions so it is important to see as many different types as possible.

Click here to download the solutions to these examples.

 

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