to "rationalize" it is to transform it into a rational number (that is a number that can be described as a/b, and is not an endless sequence of digits after the decimal point without a repeating pattern).

a square root of a not square number is irrational (not rational).

so, what this question is asking us to get rid of the square root part in the denominator (the bottom part).

for this we need to multiply to and bottom with the same expression (to keep the whole value of the quotient the same) that, when multiplied at the bottom, eliminates the square root.

what can I multiply a square root with to eliminate the square root ? the square root again - we are squaring the square root.

so, what works for 9 - sqrt(14) as factor ?

we cannot just square this as

(9- sqrt(14))² = 81 -2sqrt(14) + 14

we still have the square root included.

but remember the little trick :

(a+b)(a-b) = a² - b²

without any mixed elements.

so, we need to multiply (9-sqrt(14)) by (9+sqrt(14)) to get

81-14 = 67 which is a rational number.

therefore, the third answer option is correct.

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3 years ago