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HallsofIvy said:What, exactly, do you mean by "continued decimal number"? If you mean simply that it is not a terminating decimal, a rational number such as 1/3 has that property. That's not the reason [tex]2\sqrt{7}+ 4[/tex] is irrational.
First, the rational numbers are "closed under subtraction and division" so if [tex]x= 2\sqrt{7}+ 4[/tex] were rational so would be [tex]\sqrt{7}= (x- 4)/2[/tex]. And if [tex]\sqrt{7}[/tex] were rational then there would exist integers, a and b, with no common factors, such that [tex]\sqrt{7}= \frac{a}{b}[/tex]. From that [tex]7= \frac{a^2}{b^2}[/tex] and [tex]a^2= 7b^2[/tex]. That is, [tex]a^2[/tex] has a factor of 7 and, since 7 is a prime number, a has a factor of 7. a= 7n for some integer n so [tex]a^2= 49n^2= 7b^2[/tex]. Then [tex]b^2= 7n^2[/tex] so, as before, b has a factor of 7, contradicting the fact that a and b has no factors in common.
A rational number is any number that can be expressed as a ratio of two integers (numbers without decimal points or fractions). This includes whole numbers, fractions, and terminating or repeating decimals.
To determine if a number is rational, you can check if it can be written as a fraction in its simplest form. If the number can be expressed as a ratio of two integers, then it is rational.
No, 2√(7)+4 is not a rational number. This is because the square root of 7 is an irrational number (a number that cannot be expressed as a ratio of two integers), and when added to 4, the result is still irrational.
Yes, a rational number can be written in radical form. For example, the rational number 3/4 can be written as √(9)/√(16).
The main difference between rational and irrational numbers is that rational numbers can be expressed as a ratio of two integers, while irrational numbers cannot. Irrational numbers are also non-terminating and non-repeating, while rational numbers can be either terminating or repeating decimals.