Question

已知x+y+z=a,x+y+t=b,x+z+t=c,y+t+z=d,求x+y+t+z

Answer 1

x+y+z=a(1)

x+y+t=b(2)

x+z+t=c(3)

y+t+z=d(4)

(1)+(2)+(3)+(4)得：3x+3y+3t+3z=a+b+c+d

所以,x+y+t+z=(a+b+c+d)/3

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