Why Does $\Sigma_{i=1}^n x_i(y_i - \alpha - \beta x_1) = 0$ Follow?

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SUMMARY

The equation $\Sigma_{i=1}^n x_i(y_i - \alpha - \beta x_i) = 0$ is derived from the condition that the derivative of the negative log-likelihood function, specifically $\frac{d}{d\beta}(-\Sigma_{i=1}^n[\frac{(y_i - \alpha - \beta x_i)^2}{2 \sigma^2}])$, equals zero. This condition indicates that the estimated parameters $\alpha$ and $\beta$ minimize the residual sum of squares in a linear regression context. The derivative represents the slope of the loss function, and setting it to zero identifies the optimal values for the parameters.

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superwolf
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Why does it follow from

<br /> \frac{d}{d\beta}(-\Sigma_{i=1}^n[\frac{(y_i - \alpha - \beta x_i)^2}{2 \sigma^2}]) = 0<br />

that

<br /> \Sigma_{i=1}^n x_i(y_i - \alpha - \beta x_1) = 0<br />

?
 
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What happens when you take the derivative?

This one won't be hard ;-)
 

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