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TM TT GII TCH 12

@. B tc v i s:1. phng trnh bc 2: ax2+bx+c=0 vi x1, x2 l nghim th

ax2+bx+c = a(x-x1)(x-x2); (=b2-4ac ((=b2-ac vi b=b/2)

th

nu a+b+c=0 th x1=1; x2=c/a; nu a-b+c=0 th x1=1; x2= -c/a;

S=x1+x2= - b/a; P=x1.x2= c/a (l Vieet)

2. tam thc bc hai f(x)= ax2+bx+c

+ (0; P>0; S>0.

- th ct ox ti 4 im pb lp thnh csc ( (>0; P>0; S>0; x2 = 9x1 v s dng l Vieet.

3. Hm nht bin

Min xc nh D=R\

Tnh (>0,