From center "O" draw a radius to either endpoint of the chord.
This radius will be length "R".
From center "O" complete the radius to the intersection point of the two straight lines.
This segment of the radius will be length "R" – 8.
You have just created a right triangle.
Use Pythagoras' Theorem R2 = (R – 8)2 + 502
Multiply it out R2 = R2 –16R + 64 + 2500
Subtract R2 from both sides 0 = –16R + 64 +2500
Add 16R to both sides 16R = 64 + 2500
Add the constants 16R = 2564
Divide both sides by 16 R = 160.25
