一次函數(shù)y=ax+b的圖像過點(diǎn)(2,1),即有2a+b=1
(1)當(dāng)X=-2時,y=4a+2b+3=2(2a+b)+3=2+3=5,過定點(diǎn)(-2,5),故(1)正確
(2)對稱軸是x=-(-b)/(2a)=b/2a=(1-2a)/(2a)=1/(2a)-1.
當(dāng)X=1時,有1/(2a)-1=1,得到a=1/4.可以得到,故(2)也是正確的.
(3)當(dāng)X=0時,Y=3,過定點(diǎn)(0,3),故(3)正確.
(4)當(dāng)a>0時,頂點(diǎn)的縱坐標(biāo)是y=(4a*3-b^2)/(4a)=(12a-(1-2a)^2)/(4a)=(12a-1+4a-4a^2)/(4a)=-a-1/(4a)+4=-[a+1/(4a)]+4