In my country, Cambodia, the education is not so practical. In my class in high school, most math lessons are tough as theories alone, no practice or experiment.

Mostly, i can find the solution of a math problem, but i always questioned that why find the solution? what is it used for? What is the main purpose of complex numbers, derivation, integration, etc...? (i can't find the exact name, since my teachers use french terms in math)

Please... Any body recommend any good books or websites that explain about the uses of math.