已知s+t=21,3m-2n=9,则多项式(2s+9m)+[-(6n-2t)]=?
问题描述:
已知s+t=21,3m-2n=9,则多项式(2s+9m)+[-(6n-2t)]=?
当2y-x=5时,5(x-2y)的平方-3(-x+2y)-100=?
答
把括号去掉
(2s+9m)+[-(6n-2t)]=2s+9m-6n+2t
=2(s+t)+3(3m-2n)
=2*21+3*9
=69