考虑 means to "consider," such as to consider one's options. 思考 means to think, as in to "reflect over something". 琢磨 also means to "reflect over something," but it involves a much longer, deliberate reflection than 思考。

当简单表示“think”的时候，这三个词之间是可以互换的。 “琢磨“（注意，这里的”磨“读轻声，不读阳平），有”研究“的意思，比”思考“”考虑“的程度要深。同时，琢磨常常作动词，而思考和考虑可以作名词。 “思考”的程度又比“考虑”要深，而且“思考”更加严肃，正经。所以，思考常用于书面语，考虑在口语中用的比较多。

The first one is consider，The second one is think about The last one is ponder.

when someone thinks about a question and try to figure it out, 思考 = 考虑 for example, 请你思考一下这个问题 = 请你考虑一下这个问题 考虑 has another meaning: consider about an advice for example, 请你考虑一下我的建议 here u cant use 思考 琢磨 means to study but this is informal. for example, when he was a child, he liked to 琢磨一些电器

考虑 consider it....思考 think about it...琢磨 taste the words one by one.Hope it's easy for you to understand the emphasis point difference of them.