Question

2013.06.1.已知sinx+siny=√1.5,cosx+cosy=1.5,求cos(x-y)的值.2.设f(x)

Answer 1

(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