f(-x)=ax²-bx+3a+b
f(x)是偶函數(shù)則f(x)=f(-x)
ax²-bx+3a+b=ax²+bx+3a+b
即-b=b ,解得b=0
偶函數(shù)的定義域關(guān)于原點(diǎn)對(duì)稱
所以a-1=-2a解得a=1/3
所以f(x)=x²/3+1 (-2/3,2/3)
當(dāng)x=±2/3時(shí)f(x)=31/27
函數(shù)值域[1,31/27)
f(1/2)=13/12