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14. If [tex]$a=\frac{3+\sqrt{2}}{3-\sqrt{2}}$[/tex] and [tex]$b=\frac{3-\sqrt{2}}{3+\sqrt{2}}$[/tex], find the value of [tex][tex]$a+b$[/tex][/tex].

Sagot :

Let [tex]\( a = \frac{3+\sqrt{2}}{3-\sqrt{2}} \)[/tex] and [tex]\( b = \frac{3-\sqrt{2}}{3+\sqrt{2}} \)[/tex].

To find the sum [tex]\( a + b \)[/tex], we first rationalize the denominators of the fractions for both [tex]\( a \)[/tex] and [tex]\( b \)[/tex].

### Rationalizing [tex]\( a \)[/tex]:

[tex]\[ a = \frac{3 + \sqrt{2}}{3 - \sqrt{2}} \][/tex]

Multiply the numerator and the denominator by the conjugate of the denominator, [tex]\( 3 + \sqrt{2} \)[/tex]:

[tex]\[ a = \frac{(3 + \sqrt{2})(3 + \sqrt{2})}{(3 - \sqrt{2})(3 + \sqrt{2})} \][/tex]

Simplify the numerator and the denominator:

[tex]\[ = \frac{9 + 6\sqrt{2} + 2}{9 - 2} \][/tex]
[tex]\[ = \frac{11 + 6\sqrt{2}}{7} \][/tex]

### Rationalizing [tex]\( b \)[/tex]:

[tex]\[ b = \frac{3 - \sqrt{2}}{3 + \sqrt{2}} \][/tex]

Similarly, multiply the numerator and the denominator by the conjugate of the denominator, [tex]\( 3 - \sqrt{2} \)[/tex]:

[tex]\[ b = \frac{(3 - \sqrt{2})(3 - \sqrt{2})}{(3 + \sqrt{2})(3 - \sqrt{2})} \][/tex]

Simplify the numerator and the denominator:

[tex]\[ = \frac{9 - 6\sqrt{2} + 2}{9 - 2} \][/tex]
[tex]\[ = \frac{11 - 6\sqrt{2}}{7} \][/tex]

### Finding [tex]\( a + b \)[/tex]:

[tex]\[ a + b = \frac{11 + 6\sqrt{2}}{7} + \frac{11 - 6\sqrt{2}}{7} \][/tex]

Combine the fractions:

[tex]\[ = \frac{(11 + 6\sqrt{2}) + (11 - 6\sqrt{2})}{7} \][/tex]

Simplify the expression inside the numerator:

[tex]\[ = \frac{11 + 11}{7} \][/tex]
[tex]\[ = \frac{22}{7} \][/tex]

Thus,

[tex]\[ a + b = \frac{22}{7} \][/tex]

The value of [tex]\( \frac{22}{7} \)[/tex] is approximately [tex]\( 3.142857142857143 \)[/tex].

Therefore, the value of [tex]\( a + b \)[/tex] is:

[tex]\[ \boxed{3.142857142857143} \][/tex]