#### Answer

$x^2+y^2=49$

#### Work Step by Step

RECALL:
The standard equation of a circle whose center is at $(h, k)$ and has a radius of $r$ units is:
$(x-h)^2 + (y-k)^2 = r^2$
The given circle has its center at $(0, 0)$ and a radius of 7 units.
Thus, the standard form of the circle's equation is:
$(x-0)^2+(y-0)^2=7^2
\\x^2+y^2=49$