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: , . (σ²) I , ( ):
) : σ²=(∑(x-x¯)²/n.
) : σ²=(∑(x-x¯)²*f)/∑f
) ( ).
) , , ∑x=nx¯:
σ²=(∑(x-x¯)²/n= (∑(x²-2xx¯+x¯²))/n=(∑x²-2 ∑xx¯+ ∑x¯²)/n=(∑x²-2 ∑xx¯+ nx¯²)/n=(∑x²)/n-2x¯²+x¯².
σ²=((∑x²f)/ ∑f)-((∑xf)/ ∑f) ².
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, , :
σ²=i²(m2-m1²)=i²(((∑x1²)/∑f)-((∑x1f)/∑f)²), σ²-, ;i- ;m2=((∑ x1²)/∑f) ;m1²=((∑x1f)/∑f)²- .
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