\(x^2-4=0\)

\(\Leftrightarrow x^2=0+4\)

\(\Leftrightarrow x^2=4\)

\(\Leftrightarrow x^2=2^2\) hoặc \(x^2=\left(-2\right)^2\)

\(\Leftrightarrow x=2\) hoặc \(x=-2\)

Vậy \(x=2\) hoặc \(x=-2\).

x^2=4 -> x=2;x=-2

Gọi 3 số cần tìm lần lượt là a , b , c ( a,b,c ∈ Z )

Theo bài ra ta có :

\(\dfrac{a}{2}=\dfrac{b}{3}=\dfrac{c}{5}\) ; a+b+c=-50

Áp dụng tính chất dãy tỉ số bằng nhau ta có :

\(\dfrac{a}{2}=\dfrac{b}{3}=\dfrac{c}{5}=\dfrac{a+b+c}{2+3+5}=\dfrac{-50}{10}=-5\)

\(\Rightarrow\left\{{}\begin{matrix}a=-5.2=-10\\b=-5.3=-15\\c=-5.5=-25\end{matrix}\right.\)

a) 1,035 < 1,35

b) 1,005 < 1,050

c) 27,77 = 27,770

d) 42,5 > 42,24

a)>

b)<

c)=

d)>

3A=2.33​+6.33​+12.31​+20.33​+30.33​+42.33​

3A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}3A=1.21​+2.31​+3.41​+4.51​+5.61​+6.71​

3A=\frac{2-1}{1.2}+\frac{3-2}{2.3}+\frac{4-3}{3.4}+...+\frac{7-6}{6.7}3A=1.22−1​+2.33−2​+3.44−3​+...+6.77−6​

3A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{6}-\frac{1}{7}3A=1−21​+21​−31​+31​−41​+...+61​−71​

3A=1-\frac{1}{7}=\frac{6}{7}\Rightarrow A=\frac{2}{7}3A=1−71​=76​⇒A=72​