Example: 1, let the selling price be x yuan, then the profit per piece is X-40 yuan. Because it is said in 50 yuan that every price increase of one yuan will reduce ten pieces, the number of pieces reduced is (x-50)× 10= 10x-500. So the sales volume can be expressed as 500-( 10). It needs a profit of 8000 yuan, and the equation can be listed as (x-40) (1000-10x) = 8000. Finally, it is simplified to-10x? +1400x- 12000=0, so we can get it according to the vertex formula of quadratic function x=-b/2a.

(1) Assuming that the sales price should be X yuan, the unit profit is (x-50). Because every dollar increase will reduce 20 pieces, it is said on the basis of pricing 60 yuan, so the number of pieces reduced is (x-60)×20=20x- 1200.

So the sales volume is 800-(20x-1200) = 800-20x+1200 = 2000-20x, so the profit is 12000 yuan, and the equation (x-50) (2000-20x) = It's similar to the last question. You can simplify it and ask again.

The last question is the same. You should be able to do it in this way.