Question

若/2x-3/与/y+7/互为相反数

1.若/2x-3/与/y+7/互为相反数,则x+y-3/2=（ ）
2.已知1/3x5=1/2(1/3-1/5),1/5x7=1/2(1/5-1/7),1/7x9=1/2(1/7-1/9),则 1/2x4+1/4x6+.+1/48x50=?

Answer 1

1.若/2x-3/与/y+7/互为相反数,则x+y-3/2=（ ）
∵/2x-3/与/y+7/互为相反数
∴/2x-3/+/y+7/=0
2x-3=0 y+7=0
x=3/2 y=-7
∴x+y-3/2=3/2-7-3/2=-7
2.已知1/3x5=1/2(1/3-1/5),1/5x7=1/2(1/5-1/7),1/7x9=1/2(1/7-1/9),则 1/2x4+1/4x6+.+1/48x50
=1/2(1/2-1/4+1/4-1/6+1/6-1/8+.-1/48+1/48-1/50)
=1/2*(1/2-1/50)
=1/2*(25/50-1/50)
=1/2*24/50
=24/100
=6/25