已知函数f﹙x﹚=x²+4x+3.①若f﹙a+1﹚=0,求a的值;
f(a+1) =(a+1)^2+4(a+1)+3 =a^2+6a+8 =(a+2)(a+4) a=-2,a=-4.
已知函数f﹙x﹚=x²+4x+3.①若f﹙a+1﹚=0,求a的值; 已知f(x)=x^2+4x+3 则,f(x)=0时:x^2+4x+3=0 ===> (x+1)(x+3)=0 ===> x=-1,或者x=-3 又已知f(a+1)=0 所以:a+1=-1,或者a+1=-3 则,a=-2,或者a=-4.
因为 f﹙x﹚=x²+4x+3 所以 f﹙a+1﹚=(a+1)²+4(a+1)+3 =a²+2a+1+4a+4+3 =a²+6a+8=0 =(a+3)²-1=0 (a+3)²=1 a+3=1或-1 a=-2或-4
太简单了 让x=a+1 f(a+1)=(a+1)^2 +4(a+1)+3=a^2 +2a+1+4a+7=a^2 +6a+8 =(a+2)(a+4)=0 所以a=-2或者a=-4
f﹙a+1﹚=(a+1)^2+4(a+1)+3=(a+2)(a+4)=0, ∴a=-2,或a=-4.
∵f﹙x﹚=x²+4x+3,且f﹙a+1﹚=0,代入f﹙x﹚, 即f﹙a+1﹚=(a+1)²+4(a+1)+3=0, ∴a²+1+2a+4a+4+3=0,即a²+6a+8=0 用十字相乘法可得,(a+2)(a+4)=0 ∴a=-2或a=-4
f(a+1)=0: (a+1)^2+4(a+1)+3=0 (a+1+3)(a+1+1)=0 (a+4)(a+2)=0 a+4=0或a+2=0 a=-4或a=-2
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