Soal 1
\((-2x^2y)^3 \div x^5y \div (-2x^2y^2) = \dotso\)
(A) \(\dfrac{4}{x}\)
(B) \(\dfrac{3}{x}\)
(C) \(\dfrac{2}{x}\)
(D) \(\dfrac{y}{x}\)
(E) \(\dfrac{2y}{x}\)
Jawaban: A
Soal dapat ditulis:
\(\dfrac{(-2x^2y)^3}{x^5y \cdot (-2x^2y^2)}\)
\(\dfrac{-2^3 \cdot x^6 \cdot y^3}{-2 \cdot x^7 \cdot y^3}\)
\(\dfrac{\cancelto{4}{-8} \cdot x^6 \cdot \cancel{y^3}}{\cancel{-2} \cdot x^7 \cdot \cancel{y^3}}\)
\(\dfrac{4 \cdot x^6}{x^7}\)
\(\dfrac{4 \cdot \cancel{x^6}}{\cancelto{x}{x^7}}\)
\(\color{red}\dfrac{4}{x}\)
Soal 2
Jika \(3^x + 3^{-x} = 10\) maka nilai \(9^x + 9^{-x} = \dotso\)
(A) 95
(B) 96
(C) 97
(D) 98
(E) 100
Jawaban: D
\(3^x + 3^{-x} = 10\:\:\:\:\:\color{blue}\text{kuadratkan kedua ruas}\)
\((3^x + 3^{-x})^2 = 10^2\)
\(3^{2x} + 2\cdot 3^x \cdot 3^{-x} + 3^{-2x} = 100\)
\(3^{2x} + 2 + 3^{-2x} = 100\)
\(3^{2x} + 3^{-2x} = 100 \:-\: 2\)
\(3^{2x} + 3^{-2x} = 98\)
Soal 3
Jika \(2^x + 2^{-x} = 7\) maka nilai \(2^{3x} + 2^{-3x} = \dotso\)
(A) 322
(B) 323
(C) 324
(D) 325
(E) 326
Jawaban: A
\(2^x + 2^{-x} = 7\:\:\:\:\:\color{blue}\text{kedua ruas dipangkatkan tiga}\)
\((2^x + 2^{-x})^3 = 7^3\)
Catatan: \(\color{blue}(a + b)^3 = a^3 + 3a^2b + 3ab^2 + b^3\)
\(2^{3x} + 3\cdot 2^{2x} \cdot 2^{-x} + 3 \cdot 2^x \cdot 2^{-2x} + 2^{-3x} = 343\)
\(2^{3x} + 2^{-3x} + 3\cdot 2^{(2x\: – \: x)}+ 3 \cdot 2^{(x \:- \:2x)} = 343\)
\(2^{3x} + 2^{-3x} + 3(2^x+ 2^{-x}) = 343\)
\(2^{3x} + 2^{-3x} + 3(7) = 343\)
\(2^{3x} + 2^{-3x} + 21 = 343\)
\(2^{3x} + 2^{-3x} = 343\:-\: 21\)
\(2^{3x} + 2^{-3x} = 322\)
Soal 4
Jika \(2^x = 3, 3^y = 4, \text{ dan } 4^z = 5\) maka nilai \(8^{1-xyz}\) adalah …
(A) \(\dfrac{8}{115}\)
(B) \(\dfrac{8}{120}\)
(C) \(\dfrac{8}{125}\)
(D) \(\dfrac{16}{125}\)
(E) \(\dfrac{32}{135}\)
Jawaban: C
\(8^{1-xyz} = \dfrac{8}{8^{xyz}}\)
\(8^{1-xyz} = \dfrac{8}{2^{3(xyz)}}\)
\(8^{1-xyz} = \dfrac{8}{2^{x(3yz)}}\)
\(8^{1-xyz} = \dfrac{8}{3^{y(3z)}}\)
\(8^{1-xyz} = \dfrac{8}{4^{3z}}\)
\(8^{1-xyz} = \dfrac{8}{5^3}\)
\(8^{1-xyz} = \dfrac{8}{125}\)
Soal 5
Bentuk sederhana dari \(\left(\dfrac{1}{x^{-1} + y^{-1}}\right)\left(\dfrac{xy^{-1}\: – \:x^{-1}{y}}{y^{-1}\: – \:x^{-1}}\right)\) adalah …
(A) \(xy\)
(B) \(\dfrac{1}{x + y}\)
(C) \(\dfrac{1}{x \: – \:y}\)
(D) \(\dfrac{xy}{x + y}\)
(E) \(\dfrac{xy}{x\: – \: y}\)
Jawaban: A
\(\left(\dfrac{1}{x^{-1} + y^{-1}}\right)\left(\dfrac{xy^{-1} \: – \:x^{-1}{y}}{y^{-1}\: – \:x^{-1}}\right)\)
\(\left(\dfrac{1}{\frac{1}{x} + \frac{1}{y}}\right)\left(\dfrac{\frac{x}{y} \: – \: \frac{y}{x}}{\frac{1}{y}\: -\: \frac{1}{x}}\right)\)
\(\left(\dfrac{1}{\frac{x + y}{xy}}\right)\left(\dfrac{\frac{x^2 \:-\: y^2}{xy}}{\frac{x\:-\:y}{xy}}\right)\)
\(\left(\dfrac{xy}{\cancel{x+y}}\right)\left(\dfrac{\frac{\cancel{(x + y)}\cancel{(x\:-\:y)}}{\cancel{xy}}}{\frac{\cancel{x\:-\:y}}{\cancel{xy}}}\right)\)
\(xy\)