[tex]\large \sf \underline{Solution - }[/tex]
[tex] \rm Given \: : \: \dfrac{7 + 3 \sqrt{5} }{3 + \sqrt{5} } - \dfrac{7 - 3 \sqrt{5} }{3 - \sqrt{5} }= a + \sqrt{5b} [/tex]
- Here, we have to find the value of a and b.
➢ Multiplying the conjugate of their denominator to both the fractions.
So,
[tex] \rm \: \implies \dfrac{7 + 3 \sqrt{5} }{3 + \sqrt{5} } - \dfrac{7 - 3 \sqrt{5} }{3 - \sqrt{5} }= a + \sqrt{5b} [/tex]
[tex] \rm \: \implies \dfrac{(7 + 3 \sqrt{5})(3 - \sqrt{5}) }{(3 + \sqrt{5} )(3 - \sqrt{5})} - \dfrac{(7 - 3 \sqrt{5}) (3 + \sqrt{5})}{(3 - \sqrt{5})(3 + \sqrt{5}) }= a + \sqrt{5b} [/tex]
We know,
[tex] \rm\implies (a - b)(a + b) = (a)^{2} - (b)^{2}[/tex]
Then,
[tex] \rm \: \implies \dfrac{(7 + 3 \sqrt{5})(3 - \sqrt{5}) }{3^{2} - ( \sqrt{5} )^{2} } - \dfrac{(7 - 3 \sqrt{5}) (3 + \sqrt{5})}{3^{2} - ( \sqrt{5} )^{2} } = a + \sqrt{5b} [/tex]
[tex] \rm \: \implies \dfrac{(7 + 3 \sqrt{5})(3 - \sqrt{5}) }{9- 5 } - \dfrac{(7 - 3 \sqrt{5}) (3 + \sqrt{5})}{9 - 5 } = a + \sqrt{5b} [/tex]
[tex] \rm \: \implies \dfrac{(7 + 3 \sqrt{5})(3 - \sqrt{5}) }{4} - \dfrac{(7 - 3 \sqrt{5}) (3 + \sqrt{5})}{4 } = a + \sqrt{5b} [/tex]
Combine both the fractions,
[tex] \rm \: \implies \dfrac{(7 + 3 \sqrt{5})(3 - \sqrt{5}) - (7 - 3 \sqrt{5}) (3 + \sqrt{5})}{4} = a + \sqrt{5b} [/tex]
[tex] \rm \: \implies \dfrac{21-7\sqrt{5}+9\sqrt{5}-15-21-7\sqrt{5}+9\sqrt{5}+15}{4}= a + \sqrt{5b} [/tex]
[tex] \rm \: \implies \dfrac{4 \sqrt{5} }{4}= a + \sqrt{5b} [/tex]
[tex] \rm \: \implies \sqrt{5} = a + \sqrt{5b} [/tex]
[tex] \rm \: : \implies 0 + \sqrt{5 \times 1} = a + \sqrt{5b} [/tex]
Therefore, we notice that
- The value of a is 0
- The value of b is 1