两道 数学题 求答案及解题步骤 10.15号考的我 希望帮忙

Jaynius

1 The rate of a certain chemical reaction is directly proportional to the square of the concentration of chemical A present and inversely proportional to the concentration of chemical B present. If the concentration of chemical B is increased by 100 percent, which of the following is closest to the percent change in the concentration of chemical A required to keep the reaction rate unchanged?

A 100%  decrease     B 50% decrease    C 40% decrease    D  40% increase  E 50% increase

2 When a certain tree was first planted, it was 4 feet tall, and the height of the tree increased by a constant amount each year for next 6 years. At the end of the 6th year, the tree was 1/5 taller than it was at the end of the 4th year. By how many feet did the height of the tree increase each year?
A 3/10   B2/5  C 1/2  D 2/3  E 6/5

onlybeata

你是没看懂题吧，其实都不难的。
你要看得懂题就不会有问题的~
第一题是说，一种化学反应的速率跟a浓度的平方成正比例，跟b的浓度成反比例。
所以你可以假设速率v=kA^2/B
当B'=2B时，v不变，此时A'=√2A约等于1.4A
所以选d
第二题列个式子：4+6X=6/5(4+4X)
x=2/3也选d