$1/$ Cho $\dfrac{a}{b}$ $=$ $\dfrac{b}{c}$ $=$ $\dfrac{c}{a}$ $(a + b + c \neq$ $0$)
CMR: $a = b = c$
$2/$ Cho
$\dfrac{x}{y + z + t}$ $=$ $\dfrac{y}{z + t +x}$ $=$ $\dfrac{z}{t+x+y}$ $=$ $\dfrac{t}{x + y +z}$
Tính : $ $P$ $=$ $\dfrac{x+y}{z+t}$ $+$ $\dfrac{y +z}{t+x}$ $+$ $\dfrac{z+t}{x+y}$ + $\dfrac{t+x}{z+y}$
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Sinh Học lớp 12
