①f(1)=f(3-2)=1+3^2=10
②log2(1/2)+log3(9)=-1+2=1
③由题知q≠1(原因q=1时,a1=a2=a3=a4=8,则S3=24)
又由S3=3a1
得a1+a2+a3=3a1
即a2+a3=2a1
即a1q+a1q^2=2a1
即q^2+q-2=0
即(q+2)(q-1)=0
解得q=-2或q=1(舍去)
又由a4=a1q^3
即a1(-2)^3=8
即a1=-1
故S10=a1(1-q^10)/(1-q)
=(-1)(1-(-2)^10)/(1-(-2))
=(-1)(1-2^10)/3
=(2^10-1)/3.
(1)f(1)=10
(2)1
(3)s3=a1+a2+a3=3a1,
a2+a3=2a1, a1q+a1q²=2a1, 得q²+q-2=0,q=1或-2
q=1时,a4=a1=8. s10=8x10=80
q=-2时,a4=a1q³=a1(-2³)=8,a1=-1
s10=-1x[1-(-2)^9]/3=-(2^9+1)/3
设t=1+x/2,则x=2t-2,
代入f (1+x/2)=x^2-x-2得
f(t)=(2t-2)^2-2t+2-2=4t^2-10t+4,
再把t换成2x-1即可.
或者直接把f (1+x/2)=x^2-x-2中的x换成4x-4得
f (2x-1)=(4x-4)^2-4x+4-2=16x^2-36x+18.
(1) f(1)=2^(-1)=1/2
(2)原式=log2 2^(-1) +log3 3²=-1+2=1
(3)S3=a1+a1q+a1q²=3a1
∴1+q+q²=3
q²+q-2=0
∴q=1或q=-2
当q=1时 a1=a4=8
∴S10=10a1=80
当q=-2时
a4=a1(-2)³=8
∴a1=-1
∴S10=a1[1-(-2)^10]/[1-(-2)]
=-1×(-1023)/3
=341