b=   (x-x)(y-y)  over (x-x)2  and on the top line both the 2nd x and y have a line over them as well as the 2nd x on the bottom.   after the equals sign there is a sideways M. 

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σ u mean this 1 ? side ways m?its the greek letter pronounced as sigma which means the sum of.xtht means mean and u see my whole handwriting is messed up npw writing to write tht letter lol. i have no idea whtyis.