MHB Rationalising Surds: Get the Answers You Need - Daniel

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To rationalize surds, the discussion focuses on simplifying the expression for √63, which is correctly simplified to 3√7. The method for finding x involves determining that x is 7, as it fits within the bounds of the perfect squares 7² and 8². For y, the discussion clarifies that it must be negative, leading to the conclusion that y is -8 after applying the appropriate inequalities. The distinction between integers and natural numbers is also emphasized, highlighting the need for careful consideration of the problem's requirements. This approach effectively addresses the initial question and provides clarity on the rationalization process.
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Hi All

This is my question.

View attachment 5871

I don't know how to begin working on it.

I already tried simplifying the first part to: $$ \sqrt{63} = \sqrt{7 \cdot 3^3}=\sqrt{7}\sqrt{3^2}=3\sqrt{7}$$

But this doesn't get me closer to answering the first part of the question, and I think the same technique will apply to the second part. I would be grateful for some guidance!

Thanks.

Daniel
 

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To find $x$, consider:

$$x^2\le63<(x+1)^2$$

So, think of the perfect squares that will fit the bill here:

$$7^2\le63<8^2$$

Thus, $x=7$...can you now find $y$?
 
MarkFL said:
To find $x$, consider:

$$x^2\le63<(x+1)^2$$

So, think of the perfect squares that will fit the bill here:

$$7^2\le63<8^2$$

Thus, $x=7$...can you now find $y$?

So since $$y^2=-(51)$$, $$y$$ is between 7 ($$7^2=49$$) and 8 ($$8^2=64$$), $$y=7$$?
 
The question for finding $y$ has an error in it...we are looking for an integer rather than a natural number. Natural numbers are denoted by $\mathbb{N}$ whereas integers are denoted by $\mathbb{Z}$.

We observe that $y$ must be a negative number (do you see why?), and so we can write:

$$(y+1)^2\le51<y^2$$

Since all 3 values are negative, we change the direction of the inequality when squaring.

And if we write:

$$7^2\le51<8^2$$

We may then write:

$$y^2=8^2$$

And we take the negative root here, to obtain:

$$y=-8$$

Does this make sense?
 
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