√20 the prime factors are 2, 2, 5 so -2 * √4 *√5 -2*2*√5 -4√5 is the first part , now for √125, use prime factorization , all prime factors that make up 125 is 5, 5, 5 so √125 can be separated to √25√5 and √25 = 5 so the second part is 5√5. now -4√5 - 5√5 = -9√5. therefore answer is -9√5
