y2 +8y + 16 = 0 can factor to (y+4) (y+4) = 0 so y+4 = 0 so y = -4
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y2 + 8y + 16 = y2 + 4y + 4y + 16 = y(y + 4) + 4(y + 4) = (y + 4)(y + 4) or (y + 4)2
88 + 5y - y2 66 - 3y + y2 Subtract: 22 + 8y -2y2
The standard equation of a circle with center C(h,k) and radius r is as follows:(x - h)2 + (y - k)2 = r2(x2 -2hx +h2) + (y2 - 2ky + k2)We have...x2 + y2 - 10x + 8y + 5 =0x2 - 10x + y2 + 8y + 5 =0add h2 and k2 to both sides(x2 - 10x + h2) + (y2 + 8y + k2) = -5 + h2 + k2Using the above framework we can see that 10 = 2h, h = 5Using the above framework we can see that 8 = 2k, k = 4So the formula is(x2 - 10x + 25) + (y2 + 8y + 16) = -5 + 25 + 16(x - 5)2 + (y - 4)2 = 36the center of the circle is C(5,4) and radius 6
x2 +y2 = R2 =16 = radius 2 R = 4
If that equals 16 then the radius is 4