求解一题数学

hs861013

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 the 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?

pippo_xiaos

设第四年高为x   那么根据题意第六年高为6/5X  又因为第一年高为4  所以可得到已下方程

(6/5x-x)/2=x-4/3 (因为每年成长高度恒定）求出x 在把x带回原方程 即可求出每年增长的高度

charlesyang

设每年增长x。formula4+5x)-(4+3x)/(4+3x)=1/5

by computations,x=4/7

pippo_xiaos

不好意思忘加第一年的了 应该是 (6/5x-x)/2=x-4/4  最后x=20/3 把x带回方程得到 每年增长 2/3