Cho a 17/08/2021 Bởi Sadie Cho a { "@context": "https://schema.org", "@type": "QAPage", "mainEntity": { "@type": "Question", "name": " Cho a
Đáp án: a.$P=\pm \dfrac{1}{2}$ b.$Q=\pm 3$ Giải thích các bước giải: a.$3a^2+3b^2=10ab$ $\rightarrow (3a^2-9ab)+(3b^2-ab)=0$ $\rightarrow 3a(a-3b)-b(a-3b)=0$ $\rightarrow (3a-b)(a-3b)=0$ $\rightarrow 3a-b=0\quad hoặc \quad a-3b=0$ $Nếu \quad 3a-b=0\rightarrow b=3a\rightarrow P=\dfrac{a-3a}{a+3a}=\dfrac{-1}{2}$ $Nếu \quad a-3b=0\rightarrow a=3b\rightarrow P=\dfrac{3b-b}{3b+b}=\dfrac{1}{2}$ b.$2a^2+2b^2=5ab$ $\rightarrow 2a^2-5ab+2b^2=0$ $\rightarrow 2a^2-4ab-ab+2b^2=0$ $\rightarrow 2a(a-2b)-b(a-2b)=0$ $\rightarrow (2a-b)(a-2b)=0$ $\rightarrow 2a-b=0\rightarrow b=2a\rightarrow Q=\dfrac{a+2a}{a-2a}=-3$ Hoặc $a-2b=0\rightarrow a=2b\rightarrow Q=\dfrac{2b+b}{2b-b}=3$ Bình luận
Đáp án:
a.$P=\pm \dfrac{1}{2}$
b.$Q=\pm 3$
Giải thích các bước giải:
a.$3a^2+3b^2=10ab$
$\rightarrow (3a^2-9ab)+(3b^2-ab)=0$
$\rightarrow 3a(a-3b)-b(a-3b)=0$
$\rightarrow (3a-b)(a-3b)=0$
$\rightarrow 3a-b=0\quad hoặc \quad a-3b=0$
$Nếu \quad 3a-b=0\rightarrow b=3a\rightarrow P=\dfrac{a-3a}{a+3a}=\dfrac{-1}{2}$
$Nếu \quad a-3b=0\rightarrow a=3b\rightarrow P=\dfrac{3b-b}{3b+b}=\dfrac{1}{2}$
b.$2a^2+2b^2=5ab$
$\rightarrow 2a^2-5ab+2b^2=0$
$\rightarrow 2a^2-4ab-ab+2b^2=0$
$\rightarrow 2a(a-2b)-b(a-2b)=0$
$\rightarrow (2a-b)(a-2b)=0$
$\rightarrow 2a-b=0\rightarrow b=2a\rightarrow Q=\dfrac{a+2a}{a-2a}=-3$
Hoặc $a-2b=0\rightarrow a=2b\rightarrow Q=\dfrac{2b+b}{2b-b}=3$