did not understand the explanation.
How many points of intersection does the curve x^2 + y^2 = 4 have with line x+y =2 ?
Curve x^2 + y^2 = 4 is a circle with radius 2 and the center at the origin. A line cannot have more than 2 points of intersection with a circle, so we can eliminate choices D and E. To answer the question, we can either draw a sketch or solve the system of equations. The second approach gives(2-y)^2 + y^2 = 4or 2y^2 - 4y + 4 = 4 or y^2 - 2y = 0 from where y=0 and y=2. Thus, the line and the circle intersect at points (2,0) and (0,2).
Can you please specify what part of the solution didn't you understand?
In an x-y Cartesian coordinate system, the circle with center (a, b) and radius r is the set of all points (x, y) such that:(x-a)^2+(y-b)^2=r^2
This equation of the circle follows from the Pythagorean theorem applied to any point on the circle: as shown in the diagram above, the radius is the hypotenuse of a right-angled triangle whose other sides are of length x-a and y-b. If the circle is centered at the origin (0, 0)
, then the equation simplifies to:x^2+y^2=r^2
So x^2 + y^2 = 4
is the equation of circle centered at the origin and with radius equal to 2. Now, y=2-x
is the equation of a line with x-intercept (2, 0) and y-intercept (0,2) these points are also the intercepts of given circle with X and Y axis hence at these points line and circle intersect each other.
graph.PNG [ 16.8 KiB | Viewed 1095 times ]
Answer: C (2).