(see attachment) the diameter is the diaagonal of the squar which also makes a right triangle where the diagnal is the hypotnuse
and since it is a square the legs are equal measure a^2+b^2=c^2 where legs legnth a and b an hypotnuse legnth c c=7 a=b a^2+a^2=7^2 2a^2=49 divide by 2 both sides a^2=19.5 sqrt both sides a=√19.5
the legnth of 1 side is √19.5 max or aprox 4.41588 inches
You have to distribute the negative sign for everything in the parentheses. After that you add x to the other side then add 8 to the opposite side to move them. Then your answer is 4.