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Summer Clouds moderators

27/11/2017 at 10:31
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What is the value of   \(2x^2+2y^2-4x+2y-17=0\)  when x = 3 and y = −2? 




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    Nguyễn Hiền 29/11/2017 at 08:41

    2 x 2 + 2 y 2 - 4 x + 2 y - 172x2+2y2-4x+2y-17

    = ( 2 x 2 - 4 x + 2 ) + ( 2 y 2 + 2 y ) - 19=(2x2-4x+2)+(2y2+2y)-19

    = 2 ( x - 1 ) 2 + 2 ( y 2 + y ) - 19=2(x-1)2+2(y2+y)-19    ( 1 )(1)

    Thay x = 3, y = -2 ta có:

    ( 1 ) = 2 ( 3 - 1 ) 2 + 2 ( 2 2 - 2 ) - 19(1)=2(3-1)2+2(22-2)-19

    = 2,2 2 + 2,2 - 19=2.22+2.2-19

    = 8 + 4 - 19=số 8+4-19

    = - 7=-7

     0

  • ...
    Nguyễn Thị Hải 27/11/2017 at 11:20

    \(2x^2+2y^2-4x+2y-17\)

    \(=\left(2x^2-4x+2\right)+\left(2y^2+2y\right)-19\)

    \(=2\left(x-1\right)^2+2\left(y^2+y\right)-19\)    \(\left(1\right)\)

    Thay x=3;y=-2 ta có:

    \(\left(1\right)=2\left(3-1\right)^2+2\left(2^2-2\right)-19\)

    \(=2.2^2+2.2-19\)

    \(=8+4-19\)

    \(=-7\)


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