# CAT Practice : Coordinate Geometry

If a question looks very tough, perhaps there is some special factor that simplifies it. Perhaps a particular chord is actually a diameter?

## Area of segment

Q.6: Find the area of the region that comprises all points that satisfy the two conditions x2 + y2 + 6x + 8y ≤ 0 and 4x ≥ 3y..
1. 25π
2. ${25{\pi} \over 4}$
3. ${25{\pi} \over 2}$
4. None of these

Choice C. ${25{\pi} \over 2}$

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## Detailed Solution

x2 + y2 + 6x + 8y < 0
x2 + 6x + 9 – 9 + y2 + 8y + 16 – 16 < 0
(x + 3)2 + (y + 4)2 < 25

This represents a circular region with centre (–3, –4) and radius 5 units. Substituting x = y = 0, we also see that the inequation is satisfied. This means that the circle also passes through the origin. To find out the intercepts that the circle cuts off with the axes, substitute x = 0 to find out the y–intercept and y = 0 to find out x–intercept. Thus x–intercept = –6 and y–intercept = –8.

Now, the line 4x = 3y passes through the point (–3, –4). Or this line is the diameter of the circle. The area we are looking for is the area of a semicircle.
Required area = ${25{\pi} \over 2}$.

Correct Answer: ${25{\pi} \over 2}$

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## More questions from Coordinate Geometry

Take Geometry, add one unit of algebra; take a diagram, explain it with x's and y's. For the purists, it is geometry without the romance, for the pragmatists it is Geometry with expanded scope.