how do you isolate x in 1/2x+1/5y=9
You would subtract 1/5y, and multiply both sides by 2 (1/2's reciprocal)
subtract 1/2x from each side1/5y=9-1/2xsubtract 9 from each side1/5y-9=-1/2xmultiply each side by 22/5y-18=-xmultiply each side by -1-2/5y+18=x