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 #1
avatar+26387 
+13

In triangle ABC,$${\mathtt{AB}} = {\sqrt{{\mathtt{2}}}}$$,point D is on side BC, BD=2*DC,cosDAC=$${\frac{{\mathtt{3}}{\mathtt{\,\times\,}}{\sqrt{{\mathtt{10}}}}}{{\mathtt{10}}}}$$,cosC=$${\frac{{\mathtt{2}}{\mathtt{\,\times\,}}{\sqrt{{\mathtt{5}}}}}{{\mathtt{5}}}}$$,AC+BC=?

$$\small{
\begin{array}{l}
\angle DAC = \arccos(\frac{3\cdot\sqrt{10}}{10}) = 18.4349488229\ensurement{^{\circ}}\\\\
\angle C = \arccos(\frac{2\cdot\sqrt{5}}{5}) = 26.5650511771\ensurement{^{\circ}}\\\\
\angle DAC + \angle C = 45 \ensurement{^{\circ}} \\\\
\angle ADC = 180 \ensurement{^{\circ}} -45 \ensurement{^{\circ}}
= 135\ensurement{^{\circ}}\\\\
\angle BDA = 180 \ensurement{^{\circ}} -135 \ensurement{^{\circ}}
= 45\ensurement{^{\circ}}\\\\
\end{array}
}$$

 

Now we define:

DC = x,   BD = 2x,

H = foot (of a perpendicular) from A on line BC between B and D. ($$\small{\angle BDA = 45\ensurement{^{\circ}}}$$ !!!)

h = AH

u = BH,  v = HD,  DB = u+v = 2x

 

$$\small{
\begin{array}{l}
H = \text{foot (of a perpendicular) from }~ A \text{ to line $\overline{BC}$ } \\
h = \overline{AH}\qquad
u = \overline{BH}\qquad
v = \overline{HD}\qquad
x = \overline{DC}\qquad
\overline{BC} = 3x
\end{array}
}\\\\
\small{
\begin{array}{rcl}
\tan{(45\ensurement{^{\circ}} )}=1 &=& \frac{h}{v} \\
h &=& v\\\\
\tan{(C)} = 0.5 &=& \frac{h}{v+x} \\
0.5 &=& \frac{v}{v+x} \\
v+x &=& 2v\\
v &=& x\\\\
\overline{BD} = u+v &=& 2x \\
u&=& 2x-v \\
u &=& 2x -x \\
u &=& x\\\\
u^2+h^2 &=& \sqrt{2}^2 \quad | \quad u= 2x-v\\
(2x-v)^2 + v^2 &=& 2 \quad | \quad v=x\\
(2x-x)^2 + x^2 &=& 2 \\
x^2+x^2 &=& 2\\
2x^2 &=& 2 \\
x^2 &=& 1\\
x &=& 1\\\\
\overline{BC} = 3x = 3\cdot 1 = 3\\\\
\frac {\overline{AC}}
{ \sin{(135\ensurement{^{\circ}})} }&=&\frac{x}{\sin{(DAC)}}\\\\
\frac {\overline{AC}} {\sin{(135\ensurement{^{\circ}} )}} &=&\frac{1}{ \sin{(DAC)} }\\\\
\overline{AC} &=& \frac {\sin{(135\ensurement{^{\circ}} )}} { \sin{(DAC)} } \\\\
\end{array}
}\\\\$$

 

$$\small{
\begin{array}{rcl}
\overline{AC} &=& \frac {\sin{(135\ensurement{^{\circ}} )}}
{ \sin{ ( 18.4349488229 \ensurement{^{\circ}} )} } \\\\
\overline{AC} &=& 2.23606797750 \\\\
\overline{AC}+\overline{BC}& =& 2.23606797750 +3\\\\
\mathbf{ \overline{AC}+\overline{BC}} &\mathbf{ =}& \mathbf{5.23606797750}
&\\
\hline
\end{array}
}$$

 

24.06.2015
 #4
avatar+26387 
+8

integrate ∫(2cos3x + 3sinx) / sin^3x dx

$$\small{\begin{array}{l|lll}
\int \dfrac{2\cos{(3x)} + 3\sin{(x)} } { \sin^3{(x)} }\ dx
\quad & \quad \cos{(3x)}= \cos{(x)}\cos{(2x)} -\sin(x)\sin{(2x)}\\
\quad &\quad \cos{(3x)} = \cos{(x)}[1-2\sin^2{(x)}]-\sin{(x)}\cdot 2\sin{(x)}\cos{(x)}\\
\quad &\quad \cos{(3x)} = \cos{(x)}[1-2\sin^2{(x)}]-2\sin^2{(x)}\cos{(x)}\\
\quad &\quad \cos{(3x)} = \cos{(x)}-2\cos{(x)}\sin^2{(x)}-2\sin^2{(x)}\cos{(x)}\\
\quad &\quad \cos{(3x)} = \cos{(x)}-4\cos{(x)}\sin^2{(x)}\\
=\int \dfrac{2[\cos{(x)}-4\cos{(x)}\sin^2{(x)}] + 3\sin{(x)} }{ \sin^3{(x)} }\ dx & \\
=\int \dfrac{2\cos{(x)}-8\cos{(x)}\sin^2{(x)} + 3\sin{(x)} }{ \sin^3{(x)} }\ dx & \\
= 2 \int \dfrac{ \cos{(x)} } { \sin^3{(x)} }\ dx
-8 \int \dfrac{ \cos{(x)}\sin^2{(x)} } { \sin^3{(x)} }\ dx
+3 \int \dfrac{ \sin{(x)} } { \sin^3{(x)} }\ dx & \\
= 2 \int \dfrac{ 1 } { \sin^2{(x)} }\cdot\cot{(x)}\ dx
-8 \int \dfrac{ \cos{(x)} } { \sin{(x)} }\ dx
+3 \int \dfrac{ 1 } { \sin^2{(x)} }\ dx &\\
\quad & \quad \text{Formula:} \\
\quad & \quad \boxed{ \int \frac{f'(x)}{f(x)}=\ln{(f(x))} ~~ \int \frac{\cos{(x)}}{\sin{(x)}}\ dx = \ln {( \sin{(x)} )} } \\
\quad & \quad \boxed{ (\cot{(x)})' = -\frac{1}{\sin^2{(x)}} ~~\int \frac{1}{\sin^2{(x)}}\ dx = -\cot{(x)}}\\
\quad & \quad \boxed{ \int f'(x) \cdot [f(x)]^1 = \frac{ [f(x)]^2}{2} ~~\int \dfrac{ 1 } { \sin^2{(x)} }\cdot\cot{(x)}\ dx = -\frac{\cot^2{(x)}}{2} }\\
= 2 (-\frac{\cot^2{x}}{2}) - 8 \ln {( \sin{(x)} )} + 3 (-\cot{(x)} )&\\\\
= -\cot^2{(x)} - 8\ln {( \sin{(x)} )} - 3\cot{(x)} + c_1&\\
\end{array}}\\\\\\$$

 

$$\small{\begin{array}{rcl}
\int \dfrac{2\cos{(3x)} + 3\sin{(x)} } { \sin^3{(x)} }\ dx
&=& -\cot^2{(x)} - 8\ln {( \sin{(x)} )} - 3\cot{(x)} + c_1 \quad | \quad -\cot^2{(x)}=1-\csc^2{(x)}\\\\
\int \dfrac{2\cos{(3x)} + 3\sin{(x)} } { \sin^3{(x)} }\ dx
&=& 1-\csc^2{(x)} - 8\ln {( \sin{(x)} )} - 3\cot{(x)} + c_1 \\\\
\int \dfrac{2\cos{(3x)} + 3\sin{(x)} } { \sin^3{(x)} }\ dx
&=& -\csc^2{(x)} - 8\ln {( \sin{(x)} )} - 3\cot{(x)} + (c_1+1) \quad | \quad c = c_1+1 \\\\
\int \dfrac{2\cos{(3x)} + 3\sin{(x)} } { \sin^3{(x)} }\ dx
&=& -\csc^2{(x)} - 8\ln {( \sin{(x)} )} - 3\cot{(x)} + c \\\\
\end{array}}$$

 

23.06.2015
 #2
avatar+26387 
+15

How many numbers between 1000 and 2000 leave a remainder of 3 when divided by 11 ?

 

$$\small{
\begin{array}{rcl}
1. & 1004 & \text{remainder~} 3 \\
2. & 1015 & \text{remainder~} 3\\
3. & 1026 & \text{remainder~} 3\\
4. & 1037 & \text{remainder~} 3\\
5. & 1048 & \text{remainder~} 3\\
6. & 1059 & \text{remainder~} 3\\
7. & 1070 & \text{remainder~} 3 \\
8. & 1081 & \text{remainder~} 3\\
9. & 1092 & \text{remainder~} 3\\
10. & 1103 & \text{remainder~} 3\\
11. & 1114 & \text{remainder~} 3\\
12. & 1125 & \text{remainder~} 3\\
13. & 1136 & \text{remainder~} 3\\
14. & 1147 & \text{remainder~} 3\\
15. & 1158 & \text{remainder~} 3\\
16. & 1169 & \text{remainder~} 3\\
17. & 1180 & \text{remainder~} 3\\
18. & 1191 & \text{remainder~} 3\\
19. & 1202 & \text{remainder~} 3\\
20. & 1213 & \text{remainder~} 3\\
21. & 1224 & \text{remainder~} 3\\
22. & 1235 & \text{remainder~} 3\\
23. & 1246 & \text{remainder~} 3\\
24. & 1257 & \text{remainder~} 3\\
25. & 1268 & \text{remainder~} 3\\
26. & 1279 & \text{remainder~} 3\\
27. & 1290 & \text{remainder~} 3\\
28. & 1301 & \text{remainder~} 3\\
29. & 1312 & \text{remainder~} 3\\
30. & 1323 & \text{remainder~} 3\\
31. & 1334 & \text{remainder~} 3\\
32. & 1345 & \text{remainder~} 3\\
33. & 1356 & \text{remainder~} 3\\
34. & 1367 & \text{remainder~} 3\\
35. & 1378 & \text{remainder~} 3\\
36. & 1389 & \text{remainder~} 3\\
37. & 1400 & \text{remainder~} 3\\
38. & 1411 & \text{remainder~} 3\\
39. & 1422 & \text{remainder~} 3\\
40. & 1433 & \text{remainder~} 3\\
41. & 1444 & \text{remainder~} 3\\
42. & 1455 & \text{remainder~} 3\\
43. & 1466 & \text{remainder~} 3\\
44. & 1477 & \text{remainder~} 3\\
45. & 1488 & \text{remainder~} 3\\
46. & 1499 & \text{remainder~} 3\\
47. & 1510 & \text{remainder~} 3\\
48. & 1521 & \text{remainder~} 3\\
49. & 1532 & \text{remainder~} 3\\
50. & 1543 & \text{remainder~} 3\\
51. & 1554 & \text{remainder~} 3\\
52. & 1565 & \text{remainder~} 3\\
53. & 1576 & \text{remainder~} 3\\
54. & 1587 & \text{remainder~} 3\\
55. & 1598 & \text{remainder~} 3\\
56. & 1609 & \text{remainder~} 3\\
57. & 1620 & \text{remainder~} 3\\
58. & 1631 & \text{remainder~} 3\\
59. & 1642 & \text{remainder~} 3\\
60. & 1653 & \text{remainder~} 3\\
61. & 1664 & \text{remainder~} 3\\
62. & 1675 & \text{remainder~} 3\\
63. & 1686 & \text{remainder~} 3\\
64. & 1697 & \text{remainder~} 3\\
65. & 1708 & \text{remainder~} 3\\
66. & 1719 & \text{remainder~} 3\\
67. & 1730 & \text{remainder~} 3\\
68. & 1741 & \text{remainder~} 3\\
69. & 1752 & \text{remainder~} 3\\
70. & 1763 & \text{remainder~} 3\\
71. & 1774 & \text{remainder~} 3\\
72. & 1785 & \text{remainder~} 3\\
73. & 1796 & \text{remainder~} 3\\
74. & 1807 & \text{remainder~} 3\\
75. & 1818 & \text{remainder~} 3\\
76. & 1829 & \text{remainder~} 3\\
77. & 1840 & \text{remainder~} 3\\
78. & 1851 & \text{remainder~} 3\\
79. & 1862 & \text{remainder~} 3\\
80. & 1873 & \text{remainder~} 3\\
81. & 1884 & \text{remainder~} 3\\
82. & 1895 & \text{remainder~} 3\\
83. & 1906 & \text{remainder~} 3\\
84. & 1917 & \text{remainder~} 3\\
85. & 1928 & \text{remainder~} 3\\
86. & 1939 & \text{remainder~} 3\\
87. & 1950 & \text{remainder~} 3\\
88. & 1961 & \text{remainder~} 3\\
89. & 1972 & \text{remainder~} 3\\
90. & 1983 & \text{remainder~} 3\\
91. & 1994 & \text{remainder~} 3\\
\end{array}
}$$

 

23.06.2015
 #4
avatar+26387 
+5
23.06.2015
 #4
avatar+26387 
+5

Drei bauklötze (würfel, zylinder, kegel) wurden aufeinander gestapelt. Der Kegel past genau auf den zylinder. Der durchmesser des Zylinders ist so groß wie seine Höhe. Die Kantenlänge des Würfels ist doppelt so groß, wie der Durchmesser desZylinders. der Kegel ist 3mal so hoch wie der Zylinder. Zusammen haben sie ein Volumen von 114,27cmhoch3. Welche Kantenlänge hat der Würfel und wie groß ist die oberfläche des zusammengesetzten Körpers ?

 

 

 

 

 

 

$$\small{\text{$
\begin{array}{|lcr|}
\hline
d=\mathrm{Durchmesser~Zylinder} \\
\hline
&&\\
h_{\mathrm{Kegel}} &=& 3d \\
&&\\
h_{\mathrm{Zylinder}} &=& d \\
&&\\
a_{\mathrm{Wuerfel}} &=& 2d \\
&&\\
\hline
\end{array}
\begin{array}{|lclclcl|}
\hline
&&&&&&\\
V_{\mathrm{Kegel}} &=& \frac{1}{3}\pi (\frac{d}{2})^2\cdot h_{\mathrm{Kegel}} &=& \frac{1}{3}\pi (\frac{d}{2})^2\cdot 3d = \pi (\frac{d}{2})^2\cdot d &=& \pi \dfrac{d^3}{4}\\
&&&&&&\\
V_{\mathrm{Zylinder}} &=& \pi (\frac{d}{2})^2\cdot h_{\mathrm{Zylinder}} &=& \pi (\frac{d}{2})^2\cdot d &=& \pi \dfrac{d^3}{4}\\
&&&&&&\\
V_{\mathrm{Wuerfel}} &=& a^3 &=& (2d)^3 &=& 8d^3\\
&&&&&&\\
\hline
\end{array}
$}}$$

 

$$\small{\text{$
\begin{array}{rcl}
114,27\mathrm{~cm^3} =V_{Zusammen} &=&
V_{\mathrm{Kegel}}
+ V_{\mathrm{Zylinder}}
+ V_{\mathrm{Wuerfel}} \\\\
V &=& \pi \frac{d^3}{4} + \pi \frac{d^3}{4} + 8d^3\\\\
V &=& 2\pi \frac{d^3}{4} + 8d^3 \\\\
V &=& d^3 ( \frac{\pi}{2} + 8 )\\\\
d^3 &=& \dfrac{V}{ \frac{\pi}{2} + 8 } \\\\
\mathbf{d} &\mathbf{=}& \mathbf{ \sqrt[3]{ \dfrac{V}{ \frac{\pi}{2} + 8 } } } \\\\
d & = & \sqrt[3]{ \dfrac{114,27\mathrm{~cm^3} }{ \frac{\pi}{2} + 8 } }\\\\
\mathbf{d} &\mathbf{=}& \mathbf{ 2,285571004 \mathrm{~cm} }\\\\
a_{\mathrm{Wuerfel}} &=& 2d \\\\
\mathbf{a_{\mathrm{Wuerfel}} } &\mathbf{=}& \mathbf{ 4,57114200801\mathrm{~cm} }\\\\
\end{array}
$}}\\\\$$

 

 

Berechnung der Oberfläche O :

$$\small{\text{$
\begin{array}{|lclcrcl|}
\hline
&&&&&&\\
M_{\mathrm{Kegel}} &=& \pi \cdot \frac{d}{2}\cdot s && s^2 &=& (3d)^2+ (\frac{d}{2})^2 \\
&&&&&&\\
&&&& s^2 &=& 9d^2+\frac{d^2}{4} \\
&&&&&&\\
&&&& s^2 &=& d^2 (9+\frac{1}{4}) \\
&&&&&&\\
&&&& s^2 &=& d^2 \cdot \frac{37}{4} \\
&&&&&&\\
&&&& s^2 &=& (\frac{d}{2})^2 \cdot 37 \\
&&&&&&\\
&&&& s &=& \frac{d}{2}\cdot\sqrt{37} \\
&&&&&&\\
M_{\mathrm{Kegel}} &=& \pi \cdot \frac{d}{2}\cdot \frac{d}{2}\cdot\sqrt{37} &&&=& \pi \cdot \frac{d^2}{4}\cdot\sqrt{37} \\
&&&&&&\\
M_{\mathrm{Zylinder}} &=& \pi d\cdot h_{\mathrm{Zylinder}} &=& \pi d\cdot d &=& \pi d^2\\
&&&&&&\\
O_{\mathrm{Wuerfel}} &=& 6a^2 &=& 6\cdot(2d)^2 &=& 24d^2\\
&&&&&&\\
A_{\mathrm{Kreis}} &=& \pi \cdot (\frac{d}{2})^2 &&&=& \pi\cdot \frac{d^2}{4} \\
&&&&&&\\
\hline
\end{array}
$}}$$

 

$$\small{\text{$
\begin{array}{rcl}
O_{Zusammen} &=&
M_{\mathrm{Kegel}}
+ M_{\mathrm{Zylinder}}
+ O_{\mathrm{Wuerfel}}
- A_{\mathrm{Kreis}} \\\\
&=&
\pi \cdot \frac{d^2}{4}\cdot\sqrt{37}
+ \pi d^2
+ 24d^2
- \pi\cdot \frac{d^2}{4}\\\\
&=& \frac{d^2}{4} ( \pi \cdot\sqrt{37} +4\pi + 96 -\pi ) \\\\
&=& \frac{d^2}{4} ( \pi \cdot\sqrt{37} +3\pi + 96 ) \\\\
&=& \frac{d^2}{4} [ \pi \cdot (\sqrt{37} +3 )+ 96 ] \\\\
&=& 1,30595870359\cdot 124,534340039 \\\\
\mathbf{ O_{\mathrm{Zusammen}} } &\mathbf{=}& \mathbf{162,636705270\mathrm{~cm}^2}
\end{array}
$}}$$

 

22.06.2015