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In this question, you must show all stages of your working. Solutions relying on calculator technology are not acceptable.

(i) Given:
[tex]\[ f(x) = (x + \sqrt{2})^2 + (3x - 5\sqrt{8})^2 \][/tex]

Express [tex]\( f(x) \)[/tex] in the form [tex]\( ax^2 + bx\sqrt{2} + c \)[/tex] where [tex]\( a \)[/tex], [tex]\( b \)[/tex], and [tex]\( c \)[/tex] are integers to be found.


Sagot :

Alright, to express the function [tex]\( f(x) = (x + \sqrt{2})^2 + (3x - 5\sqrt{8})^2 \)[/tex] in the form [tex]\( ax^2 + bx\sqrt{2} + c \)[/tex], we need to expand each term and then combine them.

1. Expanding [tex]\((x + \sqrt{2})^2\)[/tex]:

Let's start with the first term [tex]\((x + \sqrt{2})^2\)[/tex].

[tex]\[ (x + \sqrt{2})^2 = x^2 + 2x\sqrt{2} + (\sqrt{2})^2 \][/tex]

Since [tex]\((\sqrt{2})^2 = 2\)[/tex], we have:

[tex]\[ (x + \sqrt{2})^2 = x^2 + 2x\sqrt{2} + 2 \][/tex]

2. Expanding [tex]\((3x - 5\sqrt{8})^2\)[/tex]:

Next, let's expand the second term [tex]\( (3x - 5\sqrt{8})^2 \)[/tex].

First, simplify [tex]\(5\sqrt{8}\)[/tex]. Note that [tex]\(\sqrt{8} = \sqrt{4 \cdot 2} = 2\sqrt{2}\)[/tex], so:

[tex]\[ 5\sqrt{8} = 5 \cdot 2\sqrt{2} = 10\sqrt{2} \][/tex]

Now, expand [tex]\( (3x - 10\sqrt{2})^2 \)[/tex]:

[tex]\[ (3x - 10\sqrt{2})^2 = (3x)^2 - 2 \cdot (3x) \cdot (10\sqrt{2}) + (10\sqrt{2})^2 \][/tex]

[tex]\[ = 9x^2 - 60x\sqrt{2} + 100 \cdot 2 \][/tex]

[tex]\[ = 9x^2 - 60x\sqrt{2} + 200 \][/tex]

3. Combining the expanded terms:

Now, we combine the expanded forms of the two terms:

[tex]\[ f(x) = (x^2 + 2x\sqrt{2} + 2) + (9x^2 - 60x\sqrt{2} + 200) \][/tex]

Combine like terms:

[tex]\[ f(x) = x^2 + 9x^2 + 2x\sqrt{2} - 60x\sqrt{2} + 2 + 200 \][/tex]

Simplify:

[tex]\[ f(x) = 10x^2 - 58x\sqrt{2} + 202 \][/tex]

Thus, expressed in the form [tex]\( ax^2 + bx\sqrt{2} + c \)[/tex], we have:

[tex]\[ a = 10 \][/tex]
[tex]\[ b = -58 \][/tex]
[tex]\[ c = 202 \][/tex]

So, the final expression is:

[tex]\[ f(x) = 10x^2 - 58x\sqrt{2} + 202 \][/tex]
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