( 3 + √ 7 ) ( 3 − √ 7 ) = 2 Explanation: You can simplify this expression by using the formula for the difference of squares a 2 − b 2 = ( a − b ) ( a + b ) In your case, you ca say that a = 3 and b = √ 7 . This means that you have ( 3 + √ 7 ) ( 3 − √ 7 ) = 3 2 − ( √ 7 ) 2 = 9 − 7 = 2 Alternatively, if you don't know the formula for the difference of squares, you can rewrite this expression by expanding the parantheses ( 3 + √ 7 ) ( 3 − √ 7 ) = 3 ⋅ 3 − 3 ⋅ √ 7 + 3 ⋅ √ 7 − √ 7 ⋅ √ 7 Once again, the result will be 3 ⋅ 3 − √ 7 ⋅ √ 7 = 3 2 − 7 = 2
