Bài 1:
a)
\(x:1,5=3,5:0,5\\ x.0,5=1,5.3,5\\ x.0,5=5,25\\ x=5,25:0,5\\ x=5,25.2\\ x=10,5\)
b)
\(\dfrac{1}{2}:x=\dfrac{1}{3}:0,5\\ x.\dfrac{1}{3}=\dfrac{1}{2}.\dfrac{1}{2}\\ x=\dfrac{1}{4}.3\\ x=\dfrac{3}{4}\)
c)
\(0,3:\dfrac{3}{4}=x:0,75\\ x.\dfrac{3}{4}=0,3.0,75\\ x.\dfrac{3}{4}=0,225\\ x=0,225.\dfrac{4}{3}\\ x=0,3\)
d)
\(\dfrac{x}{-18}=\dfrac{-2}{x}\\ x^2=-18.\left(-2\right)\\ x^2=36\\ x^2=6^2\\ \Rightarrow x=\pm6\)
e)
\(\dfrac{-3}{x}=\dfrac{-x}{\dfrac{3}{25}}\\ -x.x=-3.\dfrac{3}{25}\\ -x^2=-\dfrac{9}{25}\\ \Rightarrow x^2=\left(\dfrac{3}{5}\right)^2\\ \Rightarrow x=\pm\dfrac{3}{5}\)
g)
\(\dfrac{12-x}{7}=\dfrac{x-10}{9}\\ \left(12-x\right).9=\left(x-10\right).7\\ \Leftrightarrow12.9-x.9=x.7-7.10\\ 108-x.9=x.7-70\\ -x.9-x.7=-70-108\\ -x\left(9+7\right)=-178\\ -x.16=-178\\ -x=-178.\dfrac{1}{16}\\ -x=-\dfrac{89}{8}\\ \Rightarrow x=\dfrac{89}{8}\)
Bài 2:
Ta có:
\(\dfrac{1+y}{3}=\dfrac{4+2y}{4}\\ \left(1+y\right).4=\left(4+2y\right).3\\4+4.y=12+6.y\\4y-6y=12-4\\ y\left(4-6\right)=8\\ y.\left(-2\right)=8\\ y=\dfrac{8}{-2}\\ y=-4 \)
Thay y= -4 vào \(\dfrac{4+2y}{4}=\dfrac{1+6y}{x}\)
\(\Rightarrow\dfrac{4+2.\left(-4\right)}{4}=\dfrac{1+6.\left(-4\right)}{x}\\ \dfrac{-4}{4}=\dfrac{-23}{x}\\ -1=\dfrac{-23}{x}\\ -x=-23\\ \Rightarrow x=23\)
Vậy \(x=23\\ y=-4\)
bạn học đến tỉ lệ thức rồi cơ à
mk mới học đến luỹ thừa tiết 2
sorry nha mk ko làm đc ^-^