Question

# Which of the following is the rationalising factor of 3−7√23 + 2√7 -3 - 7√2 3 + 7√2 -3 + 7√2

Solution

## The correct option is C 3 + 7√2 We know that (a+b)(a−b)=a2−b2 Now, if an expression of the form (a√b+c√d) is given, we can rationalise that expression by multiplying it with (a√b−c√d) since  (a√b+c√d)(a√b−c√d)=a2b−c2d Thus, to rationalise (3−7√2), we multiply it with 3+7√2. The expression that is multiplied with an irrational expression to obtain a rational number is called the "rationalising factor".

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