若n等于-1,则n-2n+3n-4n+5n-6n+······+99n-100n的值为______

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若n等于-1,则n-2n+3n-4n+5n-6n+······+99n-100n的值为______
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若n等于-1,则n-2n+3n-4n+5n-6n+······+99n-100n的值为______
若n等于-1,则n-2n+3n-4n+5n-6n+······+99n-100n的值为______

若n等于-1,则n-2n+3n-4n+5n-6n+······+99n-100n的值为______
1-2=-1 3-4=-1……99-100=-1 (即两个一组,和为-1)
n-2n+3n-4n+5n-6n+...+99n-100n
=50(-1)n
=-50n
=(-50)(-1)
=50
若n等于-1,则n-2n+3n-4n+5n-6n+······+99n-100n的值为( 50 )

50

n-2n+3n-4n+5n-6n+······+99n-100n=(n-2n)+(3n-4n)+(5n-6n)+······+(99n-100n)
=(-n)+(-n)+(-n)+(-n)+...........+(-n)=-50n =50