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ANEK [815]
3 years ago
13

If x=2+√5 find the value of x²-1/x²

Mathematics
2 answers:
e-lub [12.9K]3 years ago
7 0

Answer:

8\sqrt{5}

Step-by-step explanation:

x = 2 + \sqrt{5}\\\\ x^{2} = (2+ \sqrt{5})^{2} \\\\ \ \ \ \ = 2^{2}+2* \sqrt{5}*2+( \sqrt{5})^{2}\\\\

 = 4 + 4 \sqrt{5}+5\\\\= 9+4 \sqrt{5}

\frac{1}{x^{2}}=\frac{1}{9+4\sqrt{5}}\\\\=\frac{1*(9-4\sqrt{5}}{(9+4\sqrt{5})(9-4\sqrt{5})}\\\\=\frac{9-4\sqrt{5}}{9^{2}-(4\sqrt{5})^{2}}\\\\=\frac{9-4\sqrt{5}}{81-4^{2}(\sqrt{5})^{2}}\\\\=\frac{9-4\sqrt{5}}{81-16*5}\\\\=\frac{9-4\sqrt{5}}{81-80}\\\\=\frac{9-4\sqrt{5}}{1}\\\\=9-4\sqrt{5}

x^{2}-\frac{1}{x^{2}}= 9 + 4\sqrt{5} -(9 - 4\sqrt{5})\\\\

            = 9 + 4\sqrt{5} - 9 + 4\sqrt{5}\\\\= 9 - 9 + 4\sqrt{5} + 4\sqrt{5}\\\\= 8\sqrt{5}

natta225 [31]3 years ago
3 0

Answer:

{ \tt{ {x}^{2}  -  \frac{1}{ {x}^{2} } }} \\  = { \tt{ {(2 +  \sqrt{5} )}^{2} -  \frac{1}{ {(2 +  \sqrt{5}) }^{2} }  }} \\  = { \tt{ \frac{(2 +  \sqrt{5} ) {}^{4}  - 1}{ {(2 +  \sqrt{5} )}^{2}  } }} \\  = { \tt{ \frac{(9 + 4 \sqrt{5}) {}^{2}  }{ {(9 +  4\sqrt{5}) }}}} \\  = { \tt{9 + 4 \sqrt{5} }}

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Write the word sentence as an inequality. Then solve the inequality. 3/4 is greater than or equal to a number k divided by -8
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  1. \frac{3}{4} \geq \frac{k}{-8}  
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Step-by-step explanation:

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  2. Multiply each side by -8 to cancel out the -8 under k. It should now look like this: k ≥ -6

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3 years ago
Calcula en cada caso las restantes razones trigonométricas de un angulo agudo si se conoce que:
olchik [2.2K]
A) cos a = (√22)/5; tan a = (√66)/22
B) sin a = (2√2)/3; tan a = 2√2
C) sin a = (√30)/6; cos a = (√6)/6
D) sin a = 3/5; tan a = 3/4
E) sin a = (5√26)/26; cos a = (√26)/26
F) sin a = 3/5; tan a = 3/4

Explanation
The ratio for sine is opposite/hypotenuse.  This means the side opposite the angle is √3 and the hypotenuse is 5.  Using the Pythagorean theorem to find the adjacent side,
(√3)² + A² = 5²
3+A² = 25
A² = 22
A=√22
This means that cos a = adjacent/hypotenuse = (√22)/5 and tan a = opposite/adjacent = (√3)/(√22) = (√66)/22.
B)  The ratio for cosine is adjacent/hypotenuse; this means the side adjacent to the angle is 1 and the hypotenuse is 3.  Using the Pythagorean theorem to find the side opposite the angle (p),
1² + p² = 3²
1+p² = 9
p² = 8
p=√8 = 2√2
This means that sin a = opposite/hypotenuse = (2√2)/3 and tan a = opposite/adjacent = (2√2)/1 = 2√2.
C) The ratio for tangent is opposite/adjacent; this means that the side opposite the angle is √5 and the side adjacent the angle is 1.  Using the Pythagorean theorem to find the hypotenuse,
(√5)²+1² = H²
5+1=H²
6=H²
√6 = H
This means that sin a = opposite/hypotenuse = (√5)/(√6) = (√30)/6 and cos a = adjacent/hypotenuse = 1/(√6) = (√6)/6.
D)  The ratio for cosine is adjacent/hypotenuse; this means that the side adjacent the angle is 4 and the hypotenuse is 5.  Using the Pythagorean theorem to find the side opposite the angle, p:
4²+p²=5²
16+p²=25
p²=9
p=3
This means that sin a = opposite/hypotenuse = 3/5 and tan a = opposite/adjacent = 3/4.
E)  The ratio for tangent is opposite/adjacent;; this means that the side opposite the angle is 5 and the side adjacent the angle is 1.  Using the Pythagorean theorem to find the hypotenuse,
5²+1²=H²
25+1=H²
26=H²
√26 = H
This means that sin a = opposite/hypotenuse = 5/(√26) = (5√26)/26 and cos a = adjacent/hypotenuse = 1/(√26) = √26/26.
F) 0.8 = 8/10; The ratio for cosine is adjacent/hypotenuse.  This means that the side adjacent the angle is 8 and the hypotenuse is 10.  Using the Pythagorean theorem to find the side opposite the angle, p:
8²+p² = 10²
64+p² = 100
p² = 36
p=6
This means that sin a = opposite/hypotenuse = 6/10 = 3/5 and tan a = opposite/adjacent = 6/8 = 3/4.
6 0
3 years ago
Read 2 more answers
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