Perhaps you should try some spelling variations:
thien hach » thien thanh, hien hanh
toc thien » toc thieu, ton thien, duoc thien
hanh nang » anh nang, ganh nang, hanh mang
dung cong » dung trong
tap toan » tap doan, tap quan
bai toan » bai tap
nang su » dang su, nang du, nang tu

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

• The words AND, OR and NOT may confuse the search; try adding quotes: "toc thien hach - hanh nang su dung cong ((tap toan) OR (bai toan)) cao~".
• Adding a wildcard symbol may retrieve word variants: toc thien hach - hanh nang su dung cong ((tap toan) OR (bai toan)) cao*.