Réponse :
Bonjour
1)
[tex]ab=\sqrt{17+12\sqrt{2} } *\sqrt{17-12\sqrt{2} } \\ab=\sqrt{(17+12\sqrt{2})(17-12\sqrt{2}) } \\ab=\sqrt{17^{2}-(12\sqrt{2} )^{2} } =\sqrt{289-288}\\ab=\sqrt{1} =1[/tex]
2) u² = (a + b)² = a² + 2ab + b²
u² = 17 + 12√2 + 2×1 + 17 - 12√2
u² = 34 + 2 = 36
v² = (a - b)² = a² - 2ab + b²
v² = 17 + 12√2 - 2×1 + 17 - 2√2
v² = 34 - 2 = 32
donc v = √36 = 6
et v = √32 = 4√2
On a donc: a + b = 6 ⇔ a = 6 - b ⇔ a = 6 - b
a - b = 4√2 6 - b - b = 4√2 -2b = 4√2 - 6
⇔ a = 6 - b
b = 3 - 2√2
a + b = 6 ⇔ b = 6 - a ⇔ b = 6 - a
a - b = 4√2 a - 6 + a = 4√2 2a = 4√2 + 6
⇔ b = 6 - a
a = 2√2 + 3
Au final, on a donc :
a = 2√2 + 3 et b = 3 - 2√2
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Réponse :
Bonjour
1)
[tex]ab=\sqrt{17+12\sqrt{2} } *\sqrt{17-12\sqrt{2} } \\ab=\sqrt{(17+12\sqrt{2})(17-12\sqrt{2}) } \\ab=\sqrt{17^{2}-(12\sqrt{2} )^{2} } =\sqrt{289-288}\\ab=\sqrt{1} =1[/tex]
2) u² = (a + b)² = a² + 2ab + b²
u² = 17 + 12√2 + 2×1 + 17 - 12√2
u² = 34 + 2 = 36
v² = (a - b)² = a² - 2ab + b²
v² = 17 + 12√2 - 2×1 + 17 - 2√2
v² = 34 - 2 = 32
donc v = √36 = 6
et v = √32 = 4√2
On a donc: a + b = 6 ⇔ a = 6 - b ⇔ a = 6 - b
a - b = 4√2 6 - b - b = 4√2 -2b = 4√2 - 6
⇔ a = 6 - b
b = 3 - 2√2
a + b = 6 ⇔ b = 6 - a ⇔ b = 6 - a
a - b = 4√2 a - 6 + a = 4√2 2a = 4√2 + 6
⇔ b = 6 - a
a = 2√2 + 3
Au final, on a donc :
a = 2√2 + 3 et b = 3 - 2√2