Question

高二数学，这题怎么化简

Answer 1

解
令√xy=t
120t+20t^2<=3200，两边同除20
t^2+6t<=160，接着配方
t^2+6t+9<=160+9，整理一下
（t+3）^3<=169，将t=√xy带回去
（√xy+3）^3<=169，即为所求

追问

题目20没有平方呀

Answer 2

=(sinx)^4-(sinx)^2+1 =1-(sinx)^2[1-(sinx)^2] =1-(sinx)^2*(cosx)^2 =1-(sinxcosx)^2 =1-(1/4)(2sinxcosx)^2 =1-(1/4)(sin2x)^2 =(4-(sin2x)^2)/4