Find x !

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• February 2nd 2010, 03:44 PM
Perelman
Find x !
Hii !

Can You Help me For This Exercice :

http://img189.imageshack.us/img189/7995/problem003.gif

Question is : Find x !
• February 2nd 2010, 03:48 PM
e^(i*pi)
Quote:

Originally Posted by Perelman
Hii !

Can You Help me For This Exercice :

http://img189.imageshack.us/img189/7995/problem003.gif

Question is : Find x !

Note that you have two triangles and the angles in each much add up to 180

darn, never mind >.<
• February 3rd 2010, 04:22 AM
Perelman
• February 3rd 2010, 06:07 AM
Aladdin
Quote:

Originally Posted by Perelman

It's not a right triangle :~:
• February 4th 2010, 10:27 PM
chosoi
first we have B = 180 - A - C = 180 - 3x - x
then we also find that B = B1+B2 (2 small triangle from left to right)
B1 = 180 - (A + D1) = 180 - (45 + 3x) = 135 - 3x
B2 = 180 - D2 - C = 180 - (180 - 45) - x = 45 - x
since B = B1 + B2 = 135 -3x + 45 - x = 180 - 3x - x
look up on the first line ( is this look familiar?)
result B = B1 + B2 = A + C

Now we got
B = A + C
and B = 180 - A - C
so A + C = 180 -A - C
=> A + C + A + C = 180
=> 2A + 2C = 180
plug in the real value A = 3x and C = x
=> 2(3x) + 2x = 180
=> 6x + 2x = 180
=> 8x = 180
=> x = 22.5
The End!(Hi)
• February 5th 2010, 07:54 AM
Archie Meade
Quote:

Originally Posted by Perelman
Hii !

Can You Help me For This Exercice :

http://img189.imageshack.us/img189/7995/problem003.gif

Question is : Find x !

From the attached sketch

$3x+b=180^o-45^o=135^o=3(45^o)$

$x+a=180^o-135^o=45^o$

Therefore 3x+b = 3(x+a) = 3x+3a

Hence b = 3a.

When the third apex is on the circle, x=a and 3x=b=3a, so 2x=45 degrees, so x=22.5 degrees.

When it isn't...

If...

$(3x+z)=3(x+e)$

then, as

$(x+e)+c=45^o$

$(3x+z)+y=135^o=3(45^o)$

this means

$y=3c$

The third apex of triangles ABD and ABC may be anywhere on the red line,
above the horizontal.
Therefore x ranges from 0 to 45 degrees.
However, the interior triangles may no longer touch at B.

To find out if x can be any other angle than 22.5^o...

we can use the Law of Sines.

$\frac{Sin3x}{|BD|}=\frac{Sinb}{k},\ \frac{Sinx}{|BD|}=\frac{Sina}{k}$

$|BD|=\frac{kSin3x}{Sinb}=\frac{kSinx}{Sina}$

b=3a

$\frac{Sin3x}{Sin3a}=\frac{Sinx}{Sina}$

$Sin3x=3Sinx-4Sin^3x$

$\frac{3Sinx-4Sin^3x}{3Sina-4Sin^3a}=\frac{Sinx}{Sina}$

$\frac{Sinx\left(3-4Sin^2x\right)}{Sina\left(3-4Sin^2a\right)}=\frac{Sinx}{Sina}$

$3-4Sin^2x=3-4Sin^2a$

$Sin^2x=Sin^2a$

$Sinx={\pm}Sina$

As x and "a" are acute, Sinx=Sina, x=a.

Thus x=22.5 degrees.
• February 5th 2010, 01:17 PM
Opalg
Quote:

Originally Posted by Archie Meade
From the attached sketch

$3x+b=180^o-45^o=135^o=3(45^o)$

$x+a=180^o-135^o=45^o$

Therefore 3x+b = 3(x+a) = 3x+3a

Hence b = 3a.

When the third apex is on the circle, x=a and 3x=b=3a, so 2x=45 degrees, so x=22.5 degrees.

When it isn't...

If...

$(3x+z)=3(x+e)$

then, as

$(x+e)+c=45^o$

$(3x+z)+y=135^o=3(45^o)$

this means

$y=3c$

The third apex of the triangle may be anywhere on the red line,
above the horizontal.
Therefore x ranges from 0 to 45 degrees.

That argument assumes that the two green lines intersect at a point on the red line. But that is not the case. If z = 3e ≠ 0 then the two green lines will not intersect on the red line. Alternatively, if the two green lines do intersect on the red line then it is impossible to have z = 3e (or y = 3c) unless z = e = 0.

The only solution to the problem is x = 22.5º.
• February 5th 2010, 01:38 PM
Archie Meade
Yes,
i forgot to maintain the base dimensions equal, sorry!

Corrections are applied.