Question

如图，已知线段a、b，画一条线段，是他等于2a-b

Answer 1

取AB=a
BC=a
则AC=2a
然后反向作CD=b
则AD=2a-b

Answer 2

x³-1+6x³-3x-3=0
(x-1)(x²+x+1)+3(2x²-x-1)=0
(x-1)(x²+x+1)+3(2x+1)(x-1)=0
(x-1)(x²+x+1+6x+3)=0
(x-1)(x²+7x+4)=0
x-1=0,x²+7x+4=0
x=1,x=(-7-√33)/2,x=(-7+√33)/2