方程和代數式有何分別？

方程
例:3x=9
than u can solve the x [x=3]
so 方程 means u can solve it and it has \ = /

代數式
例:7y-3-14y-4
than u can simlify it but u cant solve it ..... = -7y-7 = -7(y+1)
so 代數式 means u can simlify it but u cant solve it and it doesn't have \ = /

方程有等於
代數式沒有等於
方程有answer
代數式沒有answer

方程:5+x=4
代數式:5+x
UNDERSTAND?