+f′(1)=__________.
3 [依题意知,f(1)=×1+2=,
f′(1)=,∴f(1)+f′(1)=+=3.]
8.已知函数f(x)=f′sin x+cos x,则f′=________.
- [∵f′(x)=f′cos x-sin x,
∴f′=f′cos -sin =-1,
∴f′(x)=-cos x-sin x,
∴f′=-cos -sin =-.]
三、解答题
9.求下列函数的导数.
(1)y=;(2)y=sin;
[解] (1)
(2)∵y=sin =cos x,
∴y′=(cos x)′=-sin x.
(3)∵y=2sin cos =sin x,
∴y′=(sin x)′=cos x.
10.求证:双曲线xy=1上任何一点处的切线与坐标轴围成的三角形面积