The length of the common chord of the circles x2+y2+2x+3y+1=0 and x2+y2+4x+3y+2=0 is:
Options
A.
Option A is correct
22
(Correct)
B.
Option B
2
C.
Option C
23
D.
Option D
3
Explanation
Let the two circles be S1:x2+y2+2x+3y+1=0 and S2:x2+y2+4x+3y+2=0.
The equation of the common chord (radical axis) is S1−S2=0.
(x2+y2+2x+3y+1)−(x2+y2+4x+3y+2)=0−2x−1=0⇒2x+1=0⇒x=−21.
For circle S1, the center C1=(−1,−23) and radius r1=(−1)2+(−23)2−1=1+49−1=49=23.
The distance d from the center C1 to the common chord x=−21 is d=∣−1−(−21)∣=∣−1+21∣=∣−21∣=21.
The length of half the common chord, say L/2, can be found using the Pythagorean theorem: (L/2)2=r12−d2.
L/2=r12−d2=(23)2−(21)2=49−41=48=2.
The total length of the common chord is 2×(L/2)=22.
Options B, C, and D provide incorrect lengths, as they do not result from the correct application of the distance and Pythagorean formulas.