问题
选择题
He ______ because of watching too much TV.[ ]
A. has a good eyesight
B. has good eyesight
C. has a poor eyesight
D. has poor eyesight
答案
答案:D
He ______ because of watching too much TV.[ ]
A. has a good eyesight
B. has good eyesight
C. has a poor eyesight
D. has poor eyesight
答案:D
检验方程组的解时,必须将求得的未知数的值代入方程组中的每一个方程. 例1:解方程组
思路分析:本例这两个方程中①较简单,且x、y的系数均为1,故可把①变形,把x用y表示,或把y用x来表示皆可,然后将其代入②,消去一个未知数,化成一元一次方程,进而再求出方程组的解. 把①变形为y=4-x ③ 把③代入②得:
即
∴x=
把x=
所以原方程的解是
若想知道解的是否正确,可作如下检验: 检验:把x=
所以左边=右边. 再把x=
左边
所以左边=右边. 所以
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