Упростить выражения.

a) x^6 * x^3 = x^(6+3) = x^9; b) x^18 : x^10 = x^(18-10) = x^8; c) x^25 * (x^7)^3 = x^25 * x^(7*3) = x^25 * x^21 = x^(25+21) = x^46; d) x^12 : x^6 = x^(12-6) = x^6; e) x^7 * x^4 : (x^3)^8 = x^(7+4) / x^(3*8) = x^11 / x^24 = x^(11-24) = x^(-13); f) (x^5)^4 / (x^21 * x^5) = x^(5*4) / x^(21+5) = x^20 / x^26 = x^(20-26) = x^(-6).