circle doubts

Finding the area of the equilateral triangle in terms of circle can be found in 2 ways...

Here OA is r, while angle OAB is thirty degree..

so AB/AO=cos 30

so AB = r cos 30

so side of triangle is 2AB = 2r cos 30 = r√3

now find the area of triangle which is √3/4 side²

For the second question
you have a few options, I dont know what is given in the question as known quantities,... but
if you know the center of the circle (h,k)
and one end point (a,b)

then if you take the other end point as (x,y)

then the center of the circle will be the mid point ofo these 2 points

so (x+a)/2 = h and (y+b/)2 = k

:p

It wasnt done for so long!