(1²+3²+.....+99²)-(2²+4²+...+100²)=?
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(1²+3²+...+99²)-(2²+4²+...+100²)
=1²+(3²-2²)+(5²-4²)...+(99²-98²)-100²
=1+(3+2)(3-2)+(5+4)(5-4)+...+(99+98)(99-98)-10000
=1+(3+2)+(5+4)+...+(99+98)-10000
=1+2+3+4+...+98+99-10000
= (1+99)×99÷2-10000
=100×99÷2-10000
=9900÷2-10000
=4950-10000
= - 5050
=1²+(3²-2²)+(5²-4²)...+(99²-98²)-100²
=1+(3+2)(3-2)+(5+4)(5-4)+...+(99+98)(99-98)-10000
=1+(3+2)+(5+4)+...+(99+98)-10000
=1+2+3+4+...+98+99-10000
= (1+99)×99÷2-10000
=100×99÷2-10000
=9900÷2-10000
=4950-10000
= - 5050
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