When I am memorizing kanji , I noticed these two words have the same meaning (減算 and 引き算) . Both are subtraction , isn’t! So how can I use correctly with that words? What is the difference usage.
They are mostly synonymous. The major difference being, 引き算 is the more common name for the mathematical operation called subtraction (even used by grade school kids), while 減算 is the "scientific" term. 減算 can also indicate a decrease or reduction in amount. For example, if the amount of assistance money is decreased you can say 「支援金の減算」 but not 「支援金の引き算」. FYI, the synonyms for 足し算 is 加算, 掛け算 is 乗算, and 割り算 is 除算.