The Root of the Problem
The Root of the Problem printable sheet
Alison has been exploring sums with surds. She used a spreadsheet to make columns for square roots, and then added together various combinations.
Here is one of the sums she worked out: $$\frac{1}{\sqrt{1}+ \sqrt{2}}+ \frac{1}{\sqrt{2}+ \sqrt{3}} + ... +\frac{1}{ \sqrt {99}+ \sqrt{100}}.$$
The answer surprised her!
Can you find a way to evaluate the sum without using a calculator or spreadsheet?
Click here for a hint:
When a fraction contains surds, we often choose to multiply the numerator and denominator by an expression that gets rid of any surds in the denominator.
Knowing that $(a+b)(a-b)=a^2-b^2$ might help.
Can you find other similar sums with surds that give whole number answers?
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