How do you figure the length of a chord inside of a circle?

If I have a circle that is 710' tall I go up 355' to the center of my circle. From there I go up 147' and draw my chord from one edge of my circle to the other. I then have 208' to the top of my circle left.How do I figure the length of that chord. I have a formula of, HYP^2=147^2+X^2, to get a half of the triangle and then just double it for the length of the chord, my problem is figuring the hypotenuse? This problem is based on the Astrodome in Texas. Thanks in advance.