求值域?
求值域
y=(2x²+4x-7)/(x²+2x+3)
y(x²+2x+3)=2x²+4x-7
yx²+2yx+3y-2x²-4x+7=0
(y-2)x²+2(y-2)x+3y+7=0
b²-4ac≥0
[2(y-2)]²-4(y-2)(3y+7)≥0
-8y²-20y+72≥0
2y²+5y-18y≤0
(2y+9)(y-2)≤0
y≠2
∴-9/2≤y<2
[-9/2,2)
答:原式=100(25-20cosa-20sina+16sinacosa) 设sina+cosa=t -2^0.5<=t<=2^0.5 sinacosa=(t^2-...详情>>
答:详情>>