2013.06.1.已知sinx+siny=√1.5,cosx+cosy=1.5,求cos(x-y)的值.2.设f(x)是二次多项式函数,满足f(1)=2,f'(1)=10,f(10)=11,求f(5).

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2013.06.1.已知sinx+siny=√1.5,cosx+cosy=1.5,求cos(x-y)的值.2.设f(x)是二次多项式函数,满足f(1)=2,f'(1)=10,f(10)=11,求f(5).
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2013.06.1.已知sinx+siny=√1.5,cosx+cosy=1.5,求cos(x-y)的值.2.设f(x)是二次多项式函数,满足f(1)=2,f'(1)=10,f(10)=11,求f(5).
2013.06.
1.已知sinx+siny=√1.5,cosx+cosy=1.5,求cos(x-y)的值.
2.设f(x)是二次多项式函数,满足f(1)=2,f'(1)=10,f(10)=11,求f(5).

2013.06.1.已知sinx+siny=√1.5,cosx+cosy=1.5,求cos(x-y)的值.2.设f(x)是二次多项式函数,满足f(1)=2,f'(1)=10,f(10)=11,求f(5).
(1)(sinx+siny)²=3/2
(cosx+cosy)²=9/4
两式相加可得
2+2(sinxsiny+cosxcosy)=15/4
2cos(x-y)=7/4
cos(x-y)=7/8
(2)设f(x)=ax²+bx+c
f(1)=a+b+c=2
f'(1)=2a+b=10
f(10)=100a+10b+c=11
a=-1 b=12 c=-9
f(x)=-x²+12x-9
f(5)=-25+60-9=26