Question

Fungsi f(x)=x²+ax+b bernilai minimum 3 untuk x=2,maka a+b=

Answer 1

       y = x²+ax+b
dy/dx = 2x + a; nilai ekstrim dy/dx = 0
       0 = 2x+a
        x = -a/2; subtitusi x= 2
        2 = -a/2
         a = -4

y = x²-4x+b; subtitusi (2,3)
3 = 4-8+b
b = 7

y = x²+ax+b; a= -4, b= 7
y = x²-4x+7

a+b = -4+7
       = 3