Let the abscissae of the two points P and Q on a circle be the roots of x2 – 4x – 6 = 0 and the ordinates of P and Q be the roots of y2 + 2y – 7 = 0. If PQ is a diameter of the circle x2 + y2 + 2ax + 2by + c = 0, then the value of (a + b – c) is
Let the abscissae of the two points P and Q on a circle be the roots of x2 – 4x – 6 = 0 and the ordinates of P and Q be the roots of y2 + 2y – 7 = 0. If PQ is a diameter of the circle x2 + y2 + 2ax + 2by + c = 0, then the value of (a + b – c) is
- 12
- 13
- 14
- 16
The Correct Option is A
Solution and Explanation
The correct answer is (A) : 12
Abscissae of PQ are roots of x2 – 4x – 6 = 0
Ordinates of PQ are roots of y2 + 2y – 7 = 0
and PQ is diameter
⇒ Equation of circle is \(x^2+y^2−4x+2y−13=0\)
But, given
\(x^2+y^2+2ax+2by+c=0\)
By comparison a = –2, b = 1, c = –13
⇒ a + b – c = –2 + 1 + 13 = 12
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Concepts Used:
Circle
A circle can be geometrically defined as a combination of all the points which lie at an equal distance from a fixed point called the centre. The concepts of the circle are very important in building a strong foundation in units likes mensuration and coordinate geometry. We use circle formulas in order to calculate the area, diameter, and circumference of a circle. The length between any point on the circle and its centre is its radius.
Any line that passes through the centre of the circle and connects two points of the circle is the diameter of the circle. The radius is half the length of the diameter of the circle. The area of the circle describes the amount of space that is covered by the circle and the circumference is the length of the boundary of the circle.
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