With undetermined coefficient (y2=kx+b)? Y2 and x; 20k+b = 10； 40k+b=20？ K= 1/2，b=0。
The expression is: y2 = 1/2x (0
2) Revenue = original price+unit price: y1=100+x.
2 solution:? 1)? y =( 100- 1/2X)( 100+X)？ (0 & lt= X & lt= 10)
From-1/2x, it can be seen that k in KX2 is negative, and the quadratic function is like a parabola with an opening facing I,
X 1=200, X2 =- 100, Y=0 (intersecting with the x axis), and the symmetry axis X=50.
X=50？ Maximum y = (100-25) (150) =11250.