a) Thay $x = 2$ ta có
$A = 5. 2^2 - 3 .$ l$2$l $+ 2.2 - 3 $
$= 5. 4 - 3.2 + 1 $
$= 20 - 6 + 1 $
$= 15$
Thay $x = 5$ ta có
$A = 5. 5^2 - 3.l5l + 2.5 - 3 $
= $ 5.25 - 3.5 + 10 - 3$
= $125 - 15 + 10 - 3$
$= 117$
b) l$x$l $= \frac{1}{2}$
nên $x = \frac{1}{2}$ hoặc $x = \frac{-1}{2}$
Thay $x = \frac{1}{2}$ ta có
B = $4. (\frac{1}{2})^3 - 2.( \frac{1}{2})^2 + 3. \frac{1}{2} +1$
= $4. \frac{1}{8} - 2. \frac{1}{4} + 3. \frac{1}{2} +1$
= $\frac{5}{2} $
Thay $x = \frac{-1}{2}$ ta có
B = $4. (\frac{-1}{2})^3 - 2.( \frac{-1}{2})^2 + 3. \frac{-1}{2} +1$
= $4. \frac{-1}{8} - 2. \frac{1}{4} + 3. \frac{-1}{2} +1$
= $\frac{-3}{2}$
@Team IQ vô cực
