Difference between revisions of "2017 AMC 12B Problems/Problem 18"
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<math>\frac{(4)(\frac{70}{37})}{2} = \boxed{\textbf{(D)}\ \frac{140}{37}}</math>. | <math>\frac{(4)(\frac{70}{37})}{2} = \boxed{\textbf{(D)}\ \frac{140}{37}}</math>. | ||
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+ | -Solution by Joeya | ||
==See Also== | ==See Also== |
Revision as of 20:30, 30 December 2020
Contents
Problem
The diameter of a circle of radius is extended to a point outside the circle so that . Point is chosen so that and line is perpendicular to line . Segment intersects the circle at a point between and . What is the area of ?
Solution 1
Let be the center of the circle. Note that . However, by Power of a Point, , so . Now . Since .
Solution 2: Similar triangles with Pythagorean
is the diameter of the circle, so is a right angle, and therefore by AA similarity, .
Because of this, , so .
Likewise, , so .
Thus the area of .
Solution 2b: Area shortcut
Because is and is , the ratio of the sides is , meaning the ratio of the areas is thus . We then have the proportion
Solution 3: Similar triangles without Pythagorean
Or, use similar triangles all the way, dispense with Pythagorean, and go for minimal calculation:
Draw with on . .
.
. ( ratio applied twice)
.
Solution 4: Coordinate plane method
Let be at the origin of a coordinate plane, with being located at , etc.
We can find the area of by finding the the altitude from line to point . Realize that this altitude is the coordinate of point on the coordinate plane, since the respective base of is on the -axis.
Using the diagram in solution one, the equation for circle is .
The equation for line is then , thus .
Substituting for in the equation for circle , we get:
We can solve for to determine the coordinate of point in the coordinate plane.
Expanding the expression and factoring, we get:
Our non-zero root is thus . Calculating the area of with as the length of and as the altitude, we get:
.
-Solution by Joeya
See Also
2017 AMC 12B (Problems • Answer Key • Resources) | |
Preceded by Problem 17 |
Followed by Problem 19 |
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25 | |
All AMC 12 Problems and Solutions |
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