Radicals and the Foil Method

How do you multiply these:
(9 + √10)(9 - √10)

Use the foil method when multiplying two binomials.
(9 + √10)(9 - √10)
= 9(9) + 9(-√10) + √10(9) + √10(-√10)  {used foil method}
= 81 - 9√10 + 9√10 - √100  {multiplied through}
= 81 - √100  {combined like terms}
= 81 - 10  {evaluated square root of 100 to be 10}
= 71

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