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a) \(A=\left[\left(\frac{1}{5}\right)^2\right]^{\frac{-3}{2}}-\left[2^{-3}\right]^{\frac{-2}{3}}=5^3-2^2=121\)
b) \(B=6^2+\left[\left(\frac{1}{5}\right)^{\frac{3}{4}}\right]^{-4}=6^2+5^3=161\)
c) \(C=\frac{a^{\sqrt{5}+3}.a^{\sqrt{5}\left(\sqrt{5}-1\right)}}{\left(a^{2\sqrt{2}-1}\right)^{2\sqrt{2}+1}}=\frac{a^{\sqrt{5}+3}.a^{5-\sqrt{5}}}{a^{\left(2\sqrt{2}\right)^2-1^2}}\)
\(=\frac{a^{\sqrt{5}+3+5-\sqrt{5}}}{a^{8-1}}=\frac{a^8}{a^7}=a\)
d) \(D=\left(a^{\frac{1}{2}}-b^{\frac{1}{2}}\right)^2:\left(b-2b\sqrt{\frac{b}{a}}+\frac{b^2}{a}\right)\)
\(=\left(\sqrt{a}-\sqrt{b}\right)^2:b\left[1-2\sqrt{\frac{b}{a}}+\left(\sqrt{\frac{b}{a}}\right)^2\right]\)
\(=\left(\sqrt{a}-\sqrt{b}\right)^2:b\left(1-\sqrt{b}a\right)^2\)
\(I=\frac{a^{\frac{4}{3}}-8a^{\frac{2}{3}}b}{a^{\frac{2}{3}}+2\sqrt[3]{ab}+4b^{\frac{2}{3}}}\left(1-2\sqrt[3]{\frac{b}{a}}\right)^{-1}-a^{\frac{2}{3}}=\frac{a^{\frac{1}{3}}\left(a-8b\right)}{a^{\frac{2}{3}}+2a^{\frac{1}{3}}.b^{\frac{1}{3}}+4b^{\frac{2}{3}}}\left(\frac{\sqrt[3]{a}-2\sqrt[3]{b}}{\sqrt[3]{a}}\right)^{-1}-a^{\frac{2}{3}}\)
\(=\frac{\sqrt[3]{a}\left[\left(\sqrt[3]{a}\right)^3-\left(2\sqrt[3]{b}\right)^3\right]}{a^{\frac{2}{3}}+2\sqrt[3]{ab}+4b^{\frac{2}{3}}}.\frac{\sqrt[3]{a}}{\sqrt[3]{a}-2\sqrt[3]{b}}-a^{\frac{2}{3}}\)
\(=\frac{\left(\sqrt[3]{a}\right)^2\left(\sqrt[3]{a}-2\sqrt[3]{b}\right)\left[\left(\sqrt[3]{a}\right)^2+2\sqrt[3]{ab}+\left(2\sqrt[3]{b}\right)^2\right]}{\left(\sqrt[3]{a}-a\sqrt[3]{b}\right)\left[\left(\sqrt[3]{a}\right)^2+2\sqrt[3]{ab}+\left(2\sqrt[3]{b}\right)^2\right]}-a^{\frac{2}{3}}=a^{\frac{2}{3}}-a^{\frac{2}{3}}=0\)
\(=\frac{a\sqrt{ab}+ab-ab}{a+\sqrt{ab}}.\frac{a-b}{\sqrt[4]{ab}-\sqrt{b}}.\frac{1}{\sqrt{b}+\sqrt[4]{ab}}\)
\(=\frac{a\sqrt{ab}}{a+\sqrt{ab}}.\frac{a-b}{\sqrt{ab}-b}=\frac{a\sqrt{ab}}{\sqrt{a}\left(\sqrt{a}+\sqrt{b}\right)}.\frac{\left(\sqrt{a}+\sqrt{b}\right)\left(\sqrt{a}-\sqrt{b}\right)}{\sqrt{b}\left(\sqrt{a}-\sqrt{b}\right)}=a\)
a) \(A=\frac{a^{\frac{5}{2}}\left(a^{\frac{1}{2}}-a^{\frac{-3}{2}}\right)}{a^{\frac{1}{2}}\left(a^{\frac{-1}{2}}-a^{\frac{3}{2}}\right)}=\frac{a^3-a}{1-a^2}=-a\)
Do đó : \(A=-\left(\pi-3\sqrt{2}\right)=3\sqrt{2}-\pi\)
b) Rút gọn B ta có :
\(B=\left(a^{\frac{1}{3}}+b^{\frac{1}{3}}\right)\left[\left(a^{\frac{1}{3}}\right)^2+\left(b^{\frac{1}{3}}\right)^2\right]=\left(a^{\frac{1}{3}}\right)^3+\left(b^{\frac{1}{3}}\right)^3=a+b\)
Do đó :
\(B=\left(7-\sqrt{2}\right)+\left(\sqrt{2}+3\right)=10\)
\(B=\frac{a^{\frac{1}{4}}-a^{\frac{9}{4}}}{a^{\frac{1}{4}}-a^{\frac{5}{4}}}-\frac{b^{-\frac{1}{2}}-b^{\frac{3}{2}}}{b^{\frac{1}{2}}+b^{-\frac{1}{2}}}=\frac{a^{\frac{1}{4}}\left(1-a^2\right)}{a^{\frac{1}{4}}\left(1-a\right)}-\frac{b^{-\frac{1}{2}}\left(1-b^2\right)}{b^{-\frac{1}{2}}\left(1-b\right)}\)
\(=\left(1+a\right)-\left(1-b\right)=a+b=2013-\sqrt{2}+\sqrt{2}-2015=1\)
Câu 1:
Đặt \(\sqrt{lnx+1}=t\Rightarrow lnx=t^2-1\Rightarrow\frac{dx}{x}=2tdt\)
\(\Rightarrow I=\int3t.2t.dt=6\int t^2dt=2t^3+C\)
\(=2\sqrt{\left(lnx+1\right)^3}+C=2\left(lnx+1\right)\sqrt{lnx+1}+C\)
\(=ln\left(x.e\right)^2\sqrt{ln\left(x.e\right)+0}\Rightarrow a=2;b=0\)
Câu 2:
\(\int\limits^b_ax^{-\frac{1}{2}}dx=2x^{\frac{1}{2}}|^b_a=2\left(\sqrt{b}-\sqrt{a}\right)=2\Rightarrow\sqrt{b}-\sqrt{a}=1\)
Ta có hệ: \(\left\{{}\begin{matrix}\sqrt{b}-\sqrt{a}=1\\a^2+b^2=17\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}b=4\\a=1\end{matrix}\right.\) (lưu ý loại cặp nghiệm âm do \(\frac{1}{\sqrt{x}}\) chỉ xác định trên miền (a;b) dương)
Câu 4:
\(\int\frac{3x+a}{x^2+4}dx=\frac{3}{2}\int\frac{2x}{x^2+4}dx+a\int\frac{1}{x^2+4}dx\)
\(=\frac{3}{2}ln\left(x^2+4\right)+\frac{a}{2}arctan\left(\frac{x}{2}\right)+C\)
\(\Rightarrow a=2\)
\(\Rightarrow I=\int\limits^{\frac{e}{4}}_1ln\left(x\right)dx\)
Đặt \(\left\{{}\begin{matrix}u=lnx\\dv=dx\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}du=\frac{1}{x}dx\\v=x\end{matrix}\right.\)
\(\Rightarrow I=x.lnx|^{\frac{e}{4}}_1-\int\limits^{\frac{e}{4}}_1dx=\frac{e}{4}.ln\left(\frac{e}{4}\right)-\frac{e}{4}+1=-\frac{ln\left(2^e\right)}{2}+1\)
Câu 5:
\(f'\left(x\right)=\int f''\left(x\right)dx=-\frac{1}{4}\int x^{-\frac{3}{2}}dx=\frac{1}{2\sqrt{x}}+C\)
\(f'\left(2\right)=\frac{1}{2\sqrt{2}}+C=2+\frac{1}{2\sqrt{2}}\Rightarrow C=2\)
\(\Rightarrow f'\left(x\right)=\frac{1}{2\sqrt{x}}+2\)
\(\Rightarrow f\left(x\right)=\int f'\left(x\right)dx=\int\left(\frac{1}{2\sqrt{x}}+2\right)dx=\sqrt{x}+2x+C_1\)
\(f\left(4\right)=\sqrt{4}+2.4+C_1=10\Rightarrow C_1=0\)
\(\Rightarrow f\left(x\right)=2x+\sqrt{x}\)
\(\Rightarrow F\left(x\right)=\int f\left(x\right)dx=\int\left(2x+\sqrt{x}\right)dx=x^2+\frac{2}{3}\sqrt{x^3}+C_2\)
\(F\left(1\right)=1+\frac{2}{3}+C_2=1+\frac{2}{3}\Rightarrow C_2=0\)
\(\Rightarrow F\left(x\right)=x^2+\frac{2}{3}\sqrt{x^3}\Rightarrow\int\limits^1_0\left(x^2+\frac{2}{3}\sqrt{x^3}\right)dx=\frac{3}{5}\)
\(=\left[\frac{\left(a^{\frac{1}{2}}-b^{\frac{1}{2}}\right)\left(a+a^{\frac{1}{2}}b^{\frac{1}{2}}+b\right)}{a^{\frac{1}{2}}-b^{\frac{1}{2}}}+a^{\frac{1}{2}}b^{\frac{1}{2}}\right]\left[\frac{a^{\frac{1}{2}}-b^{\frac{1}{2}}}{\left(a^{\frac{1}{2}}-b^{\frac{1}{2}}\right)\left(a^{\frac{1}{2}}+b^{\frac{1}{2}}\right)}\right]^2\)
\(=\frac{a+2a^{\frac{1}{2}}b^{\frac{1}{2}}+b}{\left(a^{\frac{1}{2}}+b^{\frac{1}{2}}\right)^2}=\frac{\left(a^{\frac{1}{2}}+b^{\frac{1}{2}}\right)^2}{\left(a^{\frac{1}{2}}+b^{\frac{1}{2}}\right)^2}=1\)
\(A=17\frac{2}{31}-\left(\frac{15}{17}+6\frac{2}{31}\right)=\left(17\frac{2}{31}-6\frac{2}{31}\right)-\frac{15}{17}=11-\frac{15}{17}=10+\left(1-\frac{15}{17}\right)=10\frac{2}{17}\)
\(B=\left(31\frac{6}{13}-36\frac{6}{13}\right)+5\frac{9}{41}=-5+5\frac{9}{41}=\frac{9}{41}\)
C=\(\left(27\frac{51}{59}-7\frac{51}{59}\right)+\frac{1}{3}=20+\frac{1}{3}=20\frac{1}{3}\)
\(D=\left(13\frac{29}{31}-2\frac{28}{31}\right)+\left(4-3\frac{7}{8}\right)=11\frac{1}{31}+\frac{1}{8}=11\frac{8+31}{31.8}=11\frac{39}{248}\)
\(D=\left(\frac{a-b}{a^{\frac{3}{4}}+a^{\frac{1}{2}}.b^{\frac{1}{4}}}-\frac{a^{\frac{1}{2}}-b^{\frac{1}{2}}}{a^{\frac{1}{4}}+b^{\frac{1}{4}}}\right):\left(a^{\frac{1}{4}}-b^{\frac{1}{4}}\right)^{-1}\sqrt{\frac{a}{b}}\)
\(=\left[\frac{a-b}{a^{\frac{1}{2}}\left(a^{\frac{1}{4}}+b^{\frac{1}{4}}\right)}-\frac{a^{\frac{1}{2}}-b^{\frac{1}{2}}}{a^{\frac{1}{4}}+b^{\frac{1}{4}}}\right]:\left(a^{\frac{1}{4}}-b^{\frac{1}{4}}\right)^{-1}\sqrt{\frac{b}{a}}\)
\(=\frac{a-b-a+a^{\frac{1}{2}}.b^{\frac{1}{2}}}{a^{\frac{1}{2}}\left(a^{\frac{1}{4}}+b^{\frac{1}{4}}\right)}.\frac{1}{\left(a^{\frac{1}{4}}-b^{\frac{1}{4}}\right)}=\frac{b^{\frac{1}{2}}}{a^{\frac{1}{2}}}\frac{\left(a^{\frac{1}{4}}-b^{\frac{1}{4}}\right)}{\left(a^{\frac{1}{4}}-b^{\frac{1}{4}}\right)}\sqrt{\frac{a}{b}}.\sqrt{\frac{a}{b}}=1\)