已知2a-5的立方根是正负3,a+2b-1的算数平方根是4求2a-3b的立方根

Question

已知2a-5的立方根是正负3,a+2b-1的算数平方根是4 求2a-3b的立方根

Answer 1

首先,不考虑题目说的立方根是正负3的问题,应该是平方根,可能只是印刷问题.————————————————————————2a - b = (±3)^2 = 9 ==> 2a - b = 9 (1) a+2b-1 = 4^2 = 16 ==> a + 2b = 17 (2) ； (1) - (2) * 2 ==> (2a - b) - (a+2b) * 2 = 9 - 17 * 2 ==> 2a - b - 2a - 4b = -25 ==> -5b = -25 ==> b = 5； (1) * 2 + (2) ==> (2a-b)*2 + (a+2b) = 9 * 2 + 17 ==> 5a = 35 ==> a = 7 ； 2a - 3b = 2 * 7 - 3 * 5 = 14-15=-1所以,2a-3b的立方根也是-1