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Find the first 4 terms, in ascending powers of x, of the binomial expansion of \( \left(3 - \frac{1}{3} x \right)^5 \) giving each term in its simplest form. - Edexcel - A-Level Maths Pure - Question 3 - 2017 - Paper 3

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Find-the-first-4-terms,-in-ascending-powers-of-x,-of-the-binomial-expansion-of--\(--\left(3---\frac{1}{3}-x-\right)^5-\)--giving-each-term-in-its-simplest-form.-Edexcel-A-Level Maths Pure-Question 3-2017-Paper 3.png

Find the first 4 terms, in ascending powers of x, of the binomial expansion of \( \left(3 - \frac{1}{3} x \right)^5 \) giving each term in its simplest form.

Worked Solution & Example Answer:Find the first 4 terms, in ascending powers of x, of the binomial expansion of \( \left(3 - \frac{1}{3} x \right)^5 \) giving each term in its simplest form. - Edexcel - A-Level Maths Pure - Question 3 - 2017 - Paper 3

Step 1

Find the First Term

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Answer

The first term of the binomial expansion is given by:

(50)(3)5(13x)0=12431=243.\binom{5}{0} \left(3\right)^{5} \left(-\frac{1}{3} x\right)^{0} = 1 \cdot 243 \cdot 1 = 243.

Thus, the first term is 243.

Step 2

Find the Second Term

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Answer

The second term is given by:

(51)(3)4(13x)1=581(13x)=135x.\binom{5}{1} \left(3\right)^{4} \left(-\frac{1}{3} x\right)^{1} = 5 \cdot 81 \cdot \left(-\frac{1}{3} x\right) = -135 x.

Thus, the second term is -135x.

Step 3

Find the Third Term

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Answer

The third term is:

(52)(3)3(13x)2=102719x2=30x2.\binom{5}{2} \left(3\right)^{3} \left(-\frac{1}{3} x\right)^{2} = 10 \cdot 27 \cdot \frac{1}{9} x^2 = 30 x^2.

Thus, the third term is 30x².

Step 4

Find the Fourth Term

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Answer

The fourth term is:

(53)(3)2(13x)3=109(127x3)=3x3.\binom{5}{3} \left(3\right)^{2} \left(-\frac{1}{3} x\right)^{3} = 10 \cdot 9 \cdot \left(-\frac{1}{27} x^3\right) = -3 x^3.

Thus, the fourth term is -3x³.

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