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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 9: rut gon( √x + √y)( √x+ √y)-( √x- √y)( √x- √y)

Toán Lớp 9: rut gon( √x + √y)( √x+ √y)-( √x- √y)( √x- √y)

Comments ( 2 )

  1. (\sqrt{x}+\sqrt{y})(\sqrt{x}+\sqrt{y})-(\sqrt{x}-\sqrt{y})(\sqrt{x}-\sqrt{y}) (x>=0,y>=0)
    =(\sqrt{x}+\sqrt{y})^2-(\sqrt{x}-\sqrt{y})^2
    =x+2\sqrt{xy}+y-x+2\sqrt{xy}-y
    =4\sqrt{xy}
     

  2. ($\sqrt[]{x}$ + $\sqrt[]{y}$)($\sqrt[]{x}$ + $\sqrt[]{y}$) – ($\sqrt[]{x}$ – $\sqrt[]{y}$)($\sqrt[]{x}$ – $\sqrt[]{y}$)
    = ($\sqrt[]{x}$ + $\sqrt[]{y}$)² – ($\sqrt[]{x}$ – $\sqrt[]{y}$)
    = ($\sqrt[]{x}$ + $\sqrt[]{y}$ – $\sqrt[]{x}$ + $\sqrt[]{y}$)($\sqrt[]{x}$ + $\sqrt[]{y}$ + $\sqrt[]{x}$ – $\sqrt[]{y}$)
    = (2. $\sqrt[]{y}$)(2. $\sqrt[]{x}$)
    = 4$\sqrt[]{xy}$ 
     

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222-9+11+12:2*14+14 = ? ( )

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