教我一道數學題1+2+3+.+100=?
1+2+3+.+100
=(1+100)*100/2
=5050
1/(a-1)+1/(a-1)(a-2)+1(a-2)(a-3).1/(a-99)(a-100)
1/(a-1)+1/(a-1)(a-2)+1(a-2)(a-3).1/(a-99)(a-100)
=1/(a-1)+1/(a-1)-1/(a-2)+1/(a-2)-1/(a-3)+.+1/(a-99)-1/(a-100)
=2/(a-1)-1/(a-100)
=[2(a-100)-2]/(a-1)(a-100)
=(2a-202)/(a-1)(a-100)
8000-1-2-3-4….-87-88-99-100一道數學題
8000-1-2-3-4….-87-88-99-100
=8000-(1+2+3…+100)
=8000-(1+100)*100/2
=8000-(1+100)*100/2
=8000-5050
=2950
問一道數學題:(-1)+2+(-3)+4+(-5)+6+…+(-99)+100.
前後兩個數相加為1,像(-1)+2=1,(-3)+4=1,兩個數為一組,有100個數,有100/2組即是50組,原式就是50個1相加,就等於50