Question

Which of the following is the radius of the circle passing through the points (-2,0),(0,4) and centre on the x - axis ?

• A. 5
• B. 8
• C. 6
• D. 9

Answer 1

Answer:

A. 5

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$(x-a)^2+y^2=r^2$

$(-2-a)^2+0=r^2$

$2+a=r$

$a^2+16=r^2$

$a^2+16=(2+a)^2$

$a^2+16=4+4a+a^2$

$4a=12$

$a=12/4=3$

$r=2+a=2+3=5$