1. sai dấu nhé 

2.a, \(\frac{45^{10}.5^{20}}{75^{15}}=\frac{\left(3^2.5\right)^{10}.5^{20}}{\left(5^2.3\right)^{15}}=\frac{3^{20}.5^{30}}{5^{30}.3^{15}}=3^5=243\)

b, \(\frac{\left(0,8\right)^5}{\left(0,4\right)^6}=\frac{\left(\frac{4}{5}\right)^5}{\left(\frac{2}{5}\right)^6}=\frac{\left(\frac{2}{5}\cdot2\right)^5}{\left(\frac{2}{5}\right)^6}=\frac{\left(\frac{2}{5}\right)^5\cdot2^5}{\left(\frac{2}{5}\right)^5\cdot\frac{2}{5}}=2^5\div\frac{2}{5}=32\cdot\frac{5}{2}=80\)

c, \(\frac{2^{15}.9^4}{6^6.8^3}=\frac{2^{15}.3^8}{2^6.3^6.2^9}=\frac{2^{15}.3^2}{2^{15}}=3^2=9\)

\(a\left(b^2-c^2\right)-b\left(a^2-c^2\right)+c\left(a^2-b^2\right)\)

\(=ab^2-ac^2-ba^2+bc^2+ca^2-cb^2\)

\(=\left(ab^2-ac^2-bc^2\right)-\left(ba^2-bc^2-ca^2\right)\)

\(=a\left(b^2-c^2\right)-bc^2-a^2\left(b-c\right)+bc^2\)

\(=a\left(b^2-c^2\right)-a^2\left(b-c\right)\)

\(=a\left(b-c\right)\left(b+c\right)-a^2\left(b-c\right)\)

\(=\left(b+c\right)\left[a\left(b-c\right)-a^2\right]\)

\(=\left(b+c\right)\left(ab-ac-a^2\right)\)

\(a\left(b^2-c^2\right)-b\left(a^2-c^2\right)+c\left(a^2-b^2\right)\)

\(=c\left(a^2-b^2\right)+a\left(b^2-c^2\right)+b\left(c^2-a^2\right)\)

\(=-c\left[\left(b^2-c^2\right)+\left(c^2-a^2\right)\right]+a\left(b^2-c^2\right)+b\left(c^2-a^2\right)\)

\(=\left(a-c\right)\left(b^2-c^2\right)+\left(b-c\right)\left(c^2-a^2\right)\)

\(=\left(a-c\right)\left(b-c\right)\left(b+c\right)+\left(b-c\right)\left(c-a\right)\left(c+a\right)\)

\(=\left(a-c\right)\left(b-c\right)\left(b-a\right)\)

Dễ thôi hai tam giác vuông ABC và DBF có chung 1 góc 45 độ(do tam giác ABC vuông cân tại A)

nên: tam giác DBF vuông cân tại B

Suy ra: BD=DF

Tương tự tam giác DEC vuông cân tại D

Suy ra: DE=CD

Có: \(DE+DF=CD+BD=BC=8.\)

\(10.\frac{25}{6}=\frac{250}{6}=\frac{125}{3}\)

Dấu . là dấu nhân 

Hk tốt

Sai bỏ qua 

Trả lời:

\(10.\frac{25}{6}=\frac{250}{6}=\frac{125}{3}\)

A=3

B=3

\(4\frac{1}{6}h\)

4 giờ 10 phút 

= 4 giờ + 10 phút

= 240 phút + 10 phút

= 250 phút

= 25/6 giờ

Bạn thiếu dấu cộng à?

Ta có:\(H=\frac{\sqrt{a}-\sqrt{b}}{\sqrt{ab}+\sqrt{bc}+\sqrt{ca}+c}+\frac{\sqrt{b}-\sqrt{c}}{\sqrt{ab}+\sqrt{bc}+\sqrt{ca}+a}+\frac{\sqrt{c}-\sqrt{a}}{\sqrt{ab}+\sqrt{bc}+\sqrt{ca}+b}\)

\(=\frac{\sqrt{a}-\sqrt{b}}{\left(\sqrt{c}+\sqrt{a}\right)\left(\sqrt{c}+\sqrt{b}\right)}+\frac{\sqrt{b}-\sqrt{c}}{\left(\sqrt{a}+\sqrt{b}\right)\left(\sqrt{a}+\sqrt{c}\right)}+\frac{\sqrt{c}-\sqrt{a}}{\left(\sqrt{b}+\sqrt{a}\right)\left(\sqrt{b}+\sqrt{c}\right)}\)

\(=\frac{a-b+b-c+c-a}{\left(\sqrt{a}+\sqrt{b}\right)\left(\sqrt{b}+\sqrt{c}\right)\left(\sqrt{c}+\sqrt{a}\right)}\)\(=0\)

Vậy \(H=0\)