Question

当X等于多少时,4分之8+X比6分之X-5的值大3?

Answer 1

(8+x)/4-(x-5)/6=3
两边乘12
24+3x-2x+10=36
x=36-24-10
x=2

Answer 2

解：Y=(cosx)^2+sinxcosx=(1+cos2x)/2+(1/2)sin2x=根号2/2sin(2x+π/4)+1/2
1.当x等于3分之8时,Y=根号2/2sin(16/3+π/4)+1/2
2.Y的单调递增区间为[-3π/8+kπ,π/8+kπ]
主要就是2倍角公式的运用。cos2x=2(cosx)^2-1=1-2(sinx)^2; sin2x=2sinxcosx