B4
Ta có $\widehat{A}$ = $90^{o}$
$\Rightarrow$ $\widehat{B}$+$\widehat{C}$+$\widehat{D}$ = $270^{o}$
Vì $\widehat{B}$ ; $\widehat{C}$ ; $\widehat{D}$ tỉ lên với 2;3;4
$\Rightarrow$$\frac{\widehat{B}}{2}$ + $\frac{\widehat{C}}{3}$ + $\frac{\widehat{D}}{4}$ = $\frac{270^{o}}{2+3+4}$ = $\frac{270^{o}}{9}$ = $30^{o}$
$\Rightarrow$ $\begin{cases} {\widehat{B}} =2 .30^{o} = 60^{o} \\{\widehat{C}}= 3.30^{o} = 90^{o}\\{\widehat{D}}= 4 . 30^{o} = 120^{o} \end{cases}$
B5
P(x) = (x² -2x +7) = (x² - 2x +1) +6 = (x-1)² + 6 ≥ 6
⇒MinP(x) = 6 ⇔ x = 1
