1/ Tìm x, y biết:
a/ x.3 = y.7 và 2x - y = 4
b/ Ix - 1I - \(\frac{1}{2}=\frac{3}{4}\)
c/ I x + 1 I + I y - 2 I = 0
d/ (22 :4) . 2x = 4
2/ Tìm GTNN của:
a/ A = 3. I2x + 1I +5
b/ B = I x - 2014I + I x - 2015I
3/ Cho \(\frac{a}{b}=\frac{c}{d}\) CMR:
\(\frac{2a-3b}{2a+3b}=\frac{2c-3d}{2c+3d}\)
\(c,Đặt\frac{a}{b}=\frac{c}{d}=k\Rightarrow a=k.b\)
\(\Rightarrow c=d.k\)
\(-Tacó:\frac{2a-3b}{2a+3b}=\frac{2k.b-3b}{2k.b+3b}=\frac{b.\left(2k-3\right)}{b\left(2k+3\right)}=\frac{2k-3}{2k+3}\left(1\right)\)
\(-Tacó:\frac{2c-3d}{2c+3d}=\frac{2d.k-3d}{2d.k+3d}=\frac{d.\left(2k-3\right)}{d.\left(2k+3\right)}=\frac{2k-3}{2k+3}\left(2\right)\)
\(Từ\left(1\right),\left(2\right)\Rightarrow\frac{2a-3b}{2a+3b}=\frac{2c-3d}{2c+3d}\)