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In the following equation, n is an integer greater than 1 - OCR - GCSE Maths - Question 20 - 2018 - Paper 1

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In the following equation, n is an integer greater than 1. $$\left( \sqrt{2} \right)^n = k \sqrt{2}$$ (a) (i) Find k when n = 7. (ii) Find n when k = 64. (b) Sho... show full transcript

Worked Solution & Example Answer:In the following equation, n is an integer greater than 1 - OCR - GCSE Maths - Question 20 - 2018 - Paper 1

Step 1

Find k when n = 7.

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Answer

To find k when n = 7, we start with the equation:

(2)7=k2\left( \sqrt{2} \right)^7 = k \sqrt{2}

This can be simplified as:

(2)7=(21/2)7=27/2=23.5=82\left( \sqrt{2} \right)^7 = \left( 2^{1/2} \right)^7 = 2^{7/2} = 2^{3.5} = 8 \sqrt{2}

Thus, we equate:

k2=82k \sqrt{2} = 8 \sqrt{2}

By dividing both sides by ( \sqrt{2} ), we find:

k=8.k = 8.

Step 2

Find n when k = 64.

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Answer

Given k = 64, we use the same equation:

(2)n=642\left( \sqrt{2} \right)^n = 64 \sqrt{2}

We can express 64 as a power of 2:

64=2664 = 2^6

So the equation becomes:

(2)n=262=26+1/2=26.5\left( \sqrt{2} \right)^n = 2^6 \sqrt{2} = 2^{6 + 1/2} = 2^{6.5}

Thus, we equate exponents:

n2=6.5\frac{n}{2} = 6.5

Multiplying both sides by 2 gives:

n=13.n = 13.

Step 3

Show that $$\frac{14}{3 - \sqrt{2}}$$ can be written in the form a + b \sqrt{2}.

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Answer

To simplify 1432\frac{14}{3 - \sqrt{2}}, we can rationalize the denominator by multiplying the numerator and denominator by the conjugate of the denominator:

14(3+2)(32)(3+2).\frac{14(3 + \sqrt{2})}{(3 - \sqrt{2})(3 + \sqrt{2})}.

The denominator simplifies as follows:

(32)(3+2)=32(2)2=92=7.(3 - \sqrt{2})(3 + \sqrt{2}) = 3^2 - (\sqrt{2})^2 = 9 - 2 = 7.

Now the expression becomes:

14(3+2)7=2(3+2)=6+22.\frac{14(3 + \sqrt{2})}{7} = 2(3 + \sqrt{2}) = 6 + 2\sqrt{2}.

Thus, we have shown that:

1432=6+22.\frac{14}{3 - \sqrt{2}} = 6 + 2\sqrt{2}.

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