解开的英文：
to untie
to undo

参考例句：

The famous mathematician is brainiac who would rather work on solving complex mathematical problems than sleep at night.
这位著名数学家十分聪明和勤奋，宁愿晚上不睡觉，也要解开复杂的数学难题。

To become untied.
被解开(或解下)

To unfasten the buttons of.
解开…的扣子

To straighten out or disentangle(a jumble or tangle;resolve.
解开理清或解开(一堆乱糟糟的或纠结成一团的东西);解开

To free of snarls;disentangle.
解开使…不再缠结于一处;把…的纠结解开

disentangle a complicated knot
解开复杂的结扣

To open(a parcel,for example;unwrap.
打开(例如包裹);解开

Untangle knitting wool,electric flex
解开缠结的毛线、电线

To loosen or undo the lacing or laces of.
松开或解开…的带子

found the riddle not possible to rede
发现那个谜不可能解开

untie是什么意思：
v. 松开；解决；解除；使自由

You're right. Maybe you shouldn't untie me.
没错，也许你是不该把我放了。

I think if someone took the snacks, they would have untied knot.
我想如果有人要拿走零食的话，他们会解开绳扣的。

The ropes were entangled so I was not able to untie the parcel
绳子缠在一起了,所以我没能解开包裹。

They untied the rope and helped him to get down from chair.
他们解开绳子，把他从椅子上扶下来。

The bow of ribbon in the little girl's hair came untied.
小姑娘头发上扎的缎带蝴蝶结散开了。

undo是什么意思：
v. 解开，松开；取消，废除，撤销；毁灭；破坏；扰乱

It is up to the doer to undo the knot.
解铃还须系铃人。

If you undo an add, the file is left undisturbed.
如果您撤消添加操作，文件将原样保留。

Error while undoing package creation.
撤消创建程序包时出错。

If you want to repair the wheels you just undo the four nuts.
如果你想修理轮子，只需拧开这4个螺母就行了。

The two most familiar types of Undo in common use today are single Undo and multiple Undo. Single Undo is the most basic variant, reversing the effects of the most recent user action, whether procedural or incremental.
现在通常用到的两个最熟悉的撤销类型是单次撤销和多次撤销，单次撤销是一种最简单的变体，恢复最近的用户动作。