1. SBMPTN 2016 TKPA Matematika Dasar Kode 350
Jika A^{2x}=2, maka \frac{A^{5x}-A^{-5x}}{A^{3x}+A^{-3x}}=
....
(A) \frac{31}{18}
(B) \frac{31}{9}
(C) \frac{32}{18}
(D) \frac{33}{9}
(E) \frac{33}{18}
Pembahasan:
A^{2x}=2
kedua ruas kalikan dengan A^{5x}
\frac{A^{5x}-A^{-5x}}{A^{3x}+A^{-3x}}
= \frac{A^{5x}-A^{-5x}}{A^{3x}+A^{-3x}}\; \cdot \: \frac{A^{5x}}{A^{5x}}
= \frac{A^{10x}-A^{0}}{A^{8x}+A^{2x}}
= \frac{\left (A^{2x} \right )^{5}-A^{0}}{\left (A^{2x} \right )^{4}+A^{2x}}
= \frac{2^{5}-1}{2^{4}+2}
= \frac{32-1}{16+2}
= \frac{31}{18}
Jawaban _________________________ (A)
2. UM UGM 2016 Kode 371
Jika \frac{1}{\sqrt{2}+\sqrt{3}+\sqrt{5}} dapat dinyatakan sebagai
\frac{a\sqrt{2}+b\sqrt{3}+c\sqrt{30}}{12}, maka a+b+c= ....
(A) 0
(B) 1
(C) 2
(D) 3
(E) 4
Pembahasan:
\frac{1}{\sqrt{2}+\sqrt{3}+\sqrt{5}}=\frac{1}{\left (\sqrt{2}+\sqrt{3} \right )+\sqrt{5}}\; \cdot \;\frac{\left ( \sqrt{2} +\sqrt{3}\right )-\sqrt{5}}{\left (\sqrt{2}+\sqrt{3} \right )-\sqrt{5}}
= \frac{\sqrt{2} +\sqrt{3}-\sqrt{5}}{\left (\sqrt{2}+\sqrt{3} \right )^{2}-\left (\sqrt{5} \right )^{2}}
= \frac{\sqrt{2} +\sqrt{3}-\sqrt{5}}{\left (\sqrt{2}\right )^{2}+2\cdot \sqrt{2}\cdot \sqrt{3}+\left ( \sqrt{3} \right )^{2}-5}
= \frac{\sqrt{2} +\sqrt{3}-\sqrt{5}}{2+2 \sqrt{6}+3-5}
= \frac{\sqrt{2} +\sqrt{3}-\sqrt{5}}{2 \sqrt{6}}
= \frac{\sqrt{2} +\sqrt{3}-\sqrt{5}}{2 \sqrt{6}}\; \cdot \; \frac{\sqrt{6}}{\sqrt{6}}
= \frac{\sqrt{2}\: .\: \sqrt{6} +\sqrt{3}\: .\: \sqrt{6}-\sqrt{5}\: \cdot\: \sqrt{6}}{2 \left (\sqrt{6} \right )^{2}}
= \frac{\sqrt{12} +\sqrt{18}-\sqrt{30}}{2 \: \cdot \: 6}
= \frac{\sqrt{4}\: \cdot \: \sqrt{3} +\sqrt{9}\: \cdot \: \sqrt{2}-\sqrt{30}}{12}
= \frac{2\sqrt{3} +3 \sqrt{2}-\sqrt{30}}{12}
= \frac{3\sqrt{2} +2 \sqrt{3}-\sqrt{30}}{12}
\frac{3\sqrt{2} +2 \sqrt{3}-\sqrt{30}}{12}=\frac{a\sqrt{2} +b \sqrt{3}+c\sqrt{30}}{12}
Jadi a=3, b=2, c=-1, maka
a+b+c = 3+2-1
= 4
Jawaban _________________________ (E)
3. UM UGM 2016 Kode 371
Jika a^{x}=b^{y}=c^{z} dan b^{2}=ac maka x = ....
(A) \frac{2yz}{y+z}
(B) \frac{2yz}{2z-y}
(C) \frac{2yz}{2y-z}
(D) \frac{yz}{2y-z}
(E) \frac{yz}{2z-y}
Pembahasan:
Misalkan a^{x}=b^{y}=c^{z}=m
maka a^{x}=m
a=m^{\frac{1}{x}}
b^{y}=m
b=m^{\frac{1}{y}}
c^{z}=m
c=m^{\frac{1}{z}}
b^{2}=ac
\left ( m^{\frac{1}{y}} \right )^{2}=m^{\frac{1}{x}}\: \cdot \: m^{\frac{1}{z}}
m^{\frac{2}{y}}=m^{\frac{1}{x}+\frac{1}{z}}
\frac{2}{y}=\frac{1}{x}+\frac{1}{z}
\frac{2}{y}-\frac{1}{z}=\frac{1}{x}
\frac{2}{y}-\frac{1}{z}=\frac{1}{x}\\ \frac{2z-y}{yz}=\frac{1}{x}
\frac{yz}{2z-y}=x
Jawaban _________________________ (E)
Jika A^{2x}=2, maka \frac{A^{5x}-A^{-5x}}{A^{3x}+A^{-3x}}=
....
(A) \frac{31}{18}
(B) \frac{31}{9}
(C) \frac{32}{18}
(D) \frac{33}{9}
(E) \frac{33}{18}
Pembahasan:
A^{2x}=2
kedua ruas kalikan dengan A^{5x}
\frac{A^{5x}-A^{-5x}}{A^{3x}+A^{-3x}}
= \frac{A^{5x}-A^{-5x}}{A^{3x}+A^{-3x}}\; \cdot \: \frac{A^{5x}}{A^{5x}}
= \frac{A^{10x}-A^{0}}{A^{8x}+A^{2x}}
= \frac{\left (A^{2x} \right )^{5}-A^{0}}{\left (A^{2x} \right )^{4}+A^{2x}}
= \frac{2^{5}-1}{2^{4}+2}
= \frac{32-1}{16+2}
= \frac{31}{18}
Jawaban _________________________ (A)
2. UM UGM 2016 Kode 371
Jika \frac{1}{\sqrt{2}+\sqrt{3}+\sqrt{5}} dapat dinyatakan sebagai
\frac{a\sqrt{2}+b\sqrt{3}+c\sqrt{30}}{12}, maka a+b+c= ....
(A) 0
(B) 1
(C) 2
(D) 3
(E) 4
Pembahasan:
\frac{1}{\sqrt{2}+\sqrt{3}+\sqrt{5}}=\frac{1}{\left (\sqrt{2}+\sqrt{3} \right )+\sqrt{5}}\; \cdot \;\frac{\left ( \sqrt{2} +\sqrt{3}\right )-\sqrt{5}}{\left (\sqrt{2}+\sqrt{3} \right )-\sqrt{5}}
= \frac{\sqrt{2} +\sqrt{3}-\sqrt{5}}{\left (\sqrt{2}+\sqrt{3} \right )^{2}-\left (\sqrt{5} \right )^{2}}
= \frac{\sqrt{2} +\sqrt{3}-\sqrt{5}}{\left (\sqrt{2}\right )^{2}+2\cdot \sqrt{2}\cdot \sqrt{3}+\left ( \sqrt{3} \right )^{2}-5}
= \frac{\sqrt{2} +\sqrt{3}-\sqrt{5}}{2+2 \sqrt{6}+3-5}
= \frac{\sqrt{2} +\sqrt{3}-\sqrt{5}}{2 \sqrt{6}}
= \frac{\sqrt{2} +\sqrt{3}-\sqrt{5}}{2 \sqrt{6}}\; \cdot \; \frac{\sqrt{6}}{\sqrt{6}}
= \frac{\sqrt{2}\: .\: \sqrt{6} +\sqrt{3}\: .\: \sqrt{6}-\sqrt{5}\: \cdot\: \sqrt{6}}{2 \left (\sqrt{6} \right )^{2}}
= \frac{\sqrt{12} +\sqrt{18}-\sqrt{30}}{2 \: \cdot \: 6}
= \frac{\sqrt{4}\: \cdot \: \sqrt{3} +\sqrt{9}\: \cdot \: \sqrt{2}-\sqrt{30}}{12}
= \frac{2\sqrt{3} +3 \sqrt{2}-\sqrt{30}}{12}
= \frac{3\sqrt{2} +2 \sqrt{3}-\sqrt{30}}{12}
\frac{3\sqrt{2} +2 \sqrt{3}-\sqrt{30}}{12}=\frac{a\sqrt{2} +b \sqrt{3}+c\sqrt{30}}{12}
Jadi a=3, b=2, c=-1, maka
a+b+c = 3+2-1
= 4
Jawaban _________________________ (E)
3. UM UGM 2016 Kode 371
Jika a^{x}=b^{y}=c^{z} dan b^{2}=ac maka x = ....
(A) \frac{2yz}{y+z}
(B) \frac{2yz}{2z-y}
(C) \frac{2yz}{2y-z}
(D) \frac{yz}{2y-z}
(E) \frac{yz}{2z-y}
Pembahasan:
Misalkan a^{x}=b^{y}=c^{z}=m
maka a^{x}=m
a=m^{\frac{1}{x}}
b^{y}=m
b=m^{\frac{1}{y}}
c^{z}=m
c=m^{\frac{1}{z}}
b^{2}=ac
\left ( m^{\frac{1}{y}} \right )^{2}=m^{\frac{1}{x}}\: \cdot \: m^{\frac{1}{z}}
m^{\frac{2}{y}}=m^{\frac{1}{x}+\frac{1}{z}}
\frac{2}{y}=\frac{1}{x}+\frac{1}{z}
\frac{2}{y}-\frac{1}{z}=\frac{1}{x}
\frac{2}{y}-\frac{1}{z}=\frac{1}{x}\\ \frac{2z-y}{yz}=\frac{1}{x}
\frac{yz}{2z-y}=x
Jawaban _________________________ (E)
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