Tangent two circles

Tangent of two circles. Before dividing his case, we note some important points about this chapter (tangent circles). Principal importance as follows:
* The line tangent to the circle perpendicular to a line to the center of the circle (a radius of a circle)
* Remember the Pythagorean formula. Because here will be used hold the Pythagorean formula. Pythagorean formula, namely:

Now we will discuss about the tangent of two circles. Divided into 2, namely:
* The line outside the common tangent
* Common tangent line in
* The line outside the common tangent



Note the picture above!
There are two circles, one circle with center and 2 with the center circle . The radius of the circle 1 we write and the radius of circle 2 we write . Long lines outside the common tangent of two circles symbolized our . The distance of two circle center (a long line connecting the center of circle 1 and circle 2) we are symbolized as
Which is called the length of common tangent line outside?
Tangent length is measured from the point of tangency on the circle 1 to the point of tangency on the circle 2. In the picture can be written as AB.
To find the length of tangent line of external, can be searched by using the formula:
or
Can we exchange the position and ?
Can. That is, we may write . It's okay to do. As long as they'll be careful with negative signs. Negative numbers when squared, then the result is positive. Likewise, positive numbers that squared the result is positive. Thus, by swapping the positions and Our calculation will be the same.
Where are these formulas?
The formula was obtained from the Pythagorean formula. We note the external tangent. Remember! tangent line is perpendicular to the radius. Note the picture!
If the tangent line is we are so touched one of the shear center of the circle, it will get a right triangle. By applying the Pythagorean theorem on right-angled triangle, with j is the hypotenuse, and sides of a long tangent penyikunya is out and the excess of his fingers.
Try using the Pythagorean formula, then the result is a formula that has been given.
* Common tangent line in



Tangent line of the two circles is a red line on the image. Of course, to find the length we can use the following formula:
or
is the length of the tangent line of
The formula is almost the same, just sign in kurungnya now is positive.

How to memorize!


How do I memorize? How do I differentiate outside the tangent formula and the tangent line in? If we like to memorize, just memorize the formula is only on the positive and negative signs.
Only the sign was different. Can be memorized in this way. If outside, the word "outside" ends with the letter r. then the formula minus. The word "in" ending in the letter m, then the formula is added.
Most of the errors students
Majority student error is to change the minus sign and added rather than on his r. That is, a sign that replaced it has worked on after j. For example, for the formula in, they write .. while for the outer formula, they write ... This is wrong. please be careful here.
Hopefully a little help.

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