Cho 4 số a, b, c, d thỏa mãn điều kiện: b^2=ac; c^2=bd (a, b, c, d \(\ne\)0; b^3 + c^3 \(\ne\)d^3
Chứng minh rằng: a^3+b^3-c^3/b^3+c^3-d^3 = (a+b-c/b+c-d)^3
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Đặt \(\frac{x}{3}=\frac{y}{5}=k\left(k≠0\right)\Rightarrow\hept{\begin{cases}x=3k\\y=5k\end{cases}}\Rightarrow A=\frac{5\left(3k\right)^2+3\left(5k\right)^2}{10\left(3k\right)^2-3\left(5k\right)^2}\)
\(\Rightarrow A=\frac{45k^2+75k^2}{90k^2-75k^2}=\frac{120k^2}{15k^2}=8\left(\text{do k ≠ 0}\right)\)
Ta có x : y : z = 2 : 3 : 4 hay \(\frac{x}{2}=\frac{y}{3}=\frac{z}{4}\)
Áp dụng tính chất dãy tỉ số bằng nhau , ta có :
\(\frac{x}{2}=\frac{y}{3}=\frac{z}{4}=\frac{2z}{8}=\frac{x+y-2z}{2+3-8}=\frac{3}{-3}=-1\)
\(\Rightarrow\hept{\begin{cases}x=-1.2=-2\\y=-1.3=-3\\x=-1.4=-4\end{cases}}\)
I think it’s necessary for secondary students to wear uniforms when they are at school because of the following reasons. Firstly, wearing uniforms encourages students to be proud of being students of their school because they are wearing the uniforms with labels bearing their school’s name. Secondly, wearing uniforms helps students feel equal in many ways, whether they are rich or poor Finally, wearing uniforms is pracal. we don’t have to think of what to wear every day. Therefore, Students in secondary schools should wear uniform.
cậu tham khảo :
I think it’s necessary for secondary students to wear uniforms when they are at school because of the following reasons. Firstly, wearing uniforms encourages students to be proud of being students of their school because they are wearing the uniforms with labels bearing their school’s name. Secondly, wearing uniforms helps students feel equal in many ways, whether they are rich or poor Finally, wearing uniforms is pracal. we don’t have to think of what to wear every day. Therefore, Students in secondary schools should wear uniform.
Làm tròn các số sau đến chữ số thập phân thứ nhất (làm tròn đến chữ số phần mười):
\(a)\)\(2,90=2,9\)
\(b)\)\(5,45\approx5,5\)
\(c)\)\(46,219\approx46,2\)
\(d)\)\(4,592\approx4,6\)
\(e)\)\(5,05\approx5,1\)
\(f)\)\(5,88\approx5,9\)
\(g)\)\(5,99\approx6,0\)
\(h)\)\(5,04\approx5,0\)
a).....\(\approx\)2,9
b).....\(\approx\)5,5
c).....\(\approx\)46,2
d).....\(\approx\)4,6
e).....\(\approx\)5,1
f).....\(\approx\)5,9
g).....\(\approx\)6,0
h).....\(\approx\)5,0.
~HT~