20 12 Jiangxi college entrance examination science mathematics, question 8, why not choose a? Question 20. Why does the triangle area use the following method? Why?

The eighth problem is to plant cucumber x mu. Y mu of leek, then x+y

Total profit = 4 * 0.55x-1.2x+0.3 * 6y-0.9y = x+0.9y.

If A plants 50 mu of cucumber and invests 600,000 yuan? More than 540 thousand?

Question 20: Draw a picture. The area of triangle is equal to the area of triangle DPF-the area of triangle PEF.

= 1/2 * PF * Xd- 1/2 * PF * Xe？