\(\sqrt{25\left(x+1\right)}=15\)

\(\Leftrightarrow25\left(x+1\right)=225\)

\(\Leftrightarrow x+1=9\)

\(\Leftrightarrow x=8\)

Vậy chọn đáp án A.

Câu 11:

\(\sqrt{75}-5\sqrt{48}+6\sqrt{12}-9\sqrt{27}\)

\(=5\sqrt{3}-20\sqrt{3}+12\sqrt{3}-27\sqrt{3}\)

\(=-30\sqrt{3}\)

Vậy chọn đáp án D.

\(a,9a^2b+12ab^3-18ab\)

\(=3ab\left(3a+4b^2-6\right)\)

\(b,x^2+2xy-25+y^2\)

\(=\left(x^2+2xy+y^2\right)-25\)

\(=\left(x+y\right)^2-5^2\)

\(=\left(x+y-5\right)\left(x+y+5\right)\)

\(2^{4-2x}=16^4\)

\(\Rightarrow2^{4-2x}=\left(2^4\right)^4\)

\(\Rightarrow2^{4-2x}=2^{16}\)

\(\Rightarrow4-2x=16\)

\(\Rightarrow-2x=12\)

\(\Rightarrow x=-6\)

Vậy: \(x=-6\)

Câu 2:

\(a,A=\left(\sqrt{7}-3\sqrt{63}+\sqrt{28}\right).\sqrt{7}\)

\(=\left(\sqrt{7}-9\sqrt{7}+2\sqrt{7}\right).\sqrt{7}\)

\(=-6\sqrt{7}.\sqrt{7}\)

\(=-42\)

\(b,B=\sqrt{14-4\sqrt{10}}-2\sqrt{14+4\sqrt{10}}\)

\(=\sqrt{\left(\sqrt{10}\right)^2-2.\sqrt{10}.2+2^2}-2\sqrt{\left(\sqrt{10}\right)^2+2.\sqrt{10}.2+2^2}\)

\(=\sqrt{\left(\sqrt{10}-2\right)^2}-2\sqrt{\left(\sqrt{10}+2\right)^2}\)

\(=\left|\sqrt{10}-2\right|-2\left|\sqrt{10}+2\right|\)

\(=\sqrt{10}-2-2\left(\sqrt{10}+2\right)\)

\(=\sqrt{10}-2-2\sqrt{10}-4\)

\(=-\sqrt{10}-6\)

\(c,C=3\sqrt{5}+\sqrt{20}-2\sqrt{125}\)

\(=3\sqrt{5}+2\sqrt{5}-10\sqrt{5}\)

\(=-5\sqrt{5}\)