Perhaps you should try some spelling variations:
phuong thong » phuong trong, phuong hoang, phuong dong
thanh dung » thanh duong, thanh tung, thanh hung
hieu lang » chieu sang, hieu quang, nhieu tang
doi hieu » doi chieu, doc hieu, doi hien
dung cua » dung luan, dung cho
den toan » dien toan, dan toan, den tran
toan cao » toan ban, toan tap

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: doi hieu lang - thanh dung cua ((phuong thong) OR (thong thong)) den toan cao~.
• Adding a wildcard symbol may retrieve word variants: doi hieu lang - thanh dung cua ((phuong thong) or (thong thong)) den toan cao*.