a.
i. Evaluate log 1 2 4 \log_{\frac{1}{2}}4 log 2 1 4 . Let y = log 1 2 4 y = \log_{\frac{1}{2}}4 y = log 2 1 4 . Then, ( 1 2 ) y = 4 (\frac{1}{2})^y = 4 ( 2 1 ) y = 4 . Since 4 = 2 2 4 = 2^2 4 = 2 2 and 1 2 = 2 − 1 \frac{1}{2} = 2^{-1} 2 1 = 2 − 1 , we have ( 2 − 1 ) y = 2 2 (2^{-1})^y = 2^2 ( 2 − 1 ) y = 2 2 , which means 2 − y = 2 2 2^{-y} = 2^2 2 − y = 2 2 . Therefore, − y = 2 -y = 2 − y = 2 , so y = − 2 y = -2 y = − 2 .
ii. Evaluate log 0.1 10 \log_{0.1}10 log 0.1 10 . Let y = log 0.1 10 y = \log_{0.1}10 y = log 0.1 10 . Then ( 0.1 ) y = 10 (0.1)^y = 10 ( 0.1 ) y = 10 . Since 0.1 = 1 10 = 10 − 1 0.1 = \frac{1}{10} = 10^{-1} 0.1 = 10 1 = 1 0 − 1 , we have ( 10 − 1 ) y = 10 (10^{-1})^y = 10 ( 1 0 − 1 ) y = 10 , which means 10 − y = 10 1 10^{-y} = 10^1 1 0 − y = 1 0 1 . Therefore, − y = 1 -y = 1 − y = 1 , so y = − 1 y = -1 y = − 1 .
b. Find the square roots of 3 − 4 i 3-4i 3 − 4 i . Let 3 − 4 i = a + b i \sqrt{3-4i} = a+bi 3 − 4 i = a + bi , where a a a and b b b are real numbers. Squaring both sides, we get 3 − 4 i = ( a + b i ) 2 = a 2 + 2 a b i − b 2 = ( a 2 − b 2 ) + 2 a b i 3-4i = (a+bi)^2 = a^2 + 2abi - b^2 = (a^2 - b^2) + 2abi 3 − 4 i = ( a + bi ) 2 = a 2 + 2 abi − b 2 = ( a 2 − b 2 ) + 2 abi . Equating the real and imaginary parts, we have:
a 2 − b 2 = 3 a^2 - b^2 = 3 a 2 − b 2 = 3 and 2 a b = − 4 2ab = -4 2 ab = − 4 , which implies a b = − 2 ab = -2 ab = − 2 , so b = − 2 a b = -\frac{2}{a} b = − a 2 . Substituting b b b into the first equation: a 2 − ( − 2 a ) 2 = 3 a^2 - (-\frac{2}{a})^2 = 3 a 2 − ( − a 2 ) 2 = 3 a 2 − 4 a 2 = 3 a^2 - \frac{4}{a^2} = 3 a 2 − a 2 4 = 3 a 4 − 4 = 3 a 2 a^4 - 4 = 3a^2 a 4 − 4 = 3 a 2 a 4 − 3 a 2 − 4 = 0 a^4 - 3a^2 - 4 = 0 a 4 − 3 a 2 − 4 = 0 Let u = a 2 u = a^2 u = a 2 . Then u 2 − 3 u − 4 = 0 u^2 - 3u - 4 = 0 u 2 − 3 u − 4 = 0 . ( u − 4 ) ( u + 1 ) = 0 (u-4)(u+1) = 0 ( u − 4 ) ( u + 1 ) = 0 . So u = 4 u = 4 u = 4 or u = − 1 u = -1 u = − 1 . Since a a a is real, a 2 a^2 a 2 must be non-negative. Therefore, a 2 = 4 a^2 = 4 a 2 = 4 , which means a = 2 a = 2 a = 2 or a = − 2 a = -2 a = − 2 . If a = 2 a = 2 a = 2 , then b = − 2 2 = − 1 b = -\frac{2}{2} = -1 b = − 2 2 = − 1 . If a = − 2 a = -2 a = − 2 , then b = − 2 − 2 = 1 b = -\frac{2}{-2} = 1 b = − − 2 2 = 1 . Therefore, the square roots are 2 − i 2-i 2 − i and − 2 + i -2+i − 2 + i .
c.
i. Express x ( x + 3 ) ( x + 2 ) \frac{x}{(x+3)(x+2)} ( x + 3 ) ( x + 2 ) x in partial fractions. We can write x ( x + 3 ) ( x + 2 ) = A x + 3 + B x + 2 \frac{x}{(x+3)(x+2)} = \frac{A}{x+3} + \frac{B}{x+2} ( x + 3 ) ( x + 2 ) x = x + 3 A + x + 2 B . Multiplying both sides by ( x + 3 ) ( x + 2 ) (x+3)(x+2) ( x + 3 ) ( x + 2 ) , we get x = A ( x + 2 ) + B ( x + 3 ) x = A(x+2) + B(x+3) x = A ( x + 2 ) + B ( x + 3 ) . If x = − 3 x = -3 x = − 3 , then − 3 = A ( − 3 + 2 ) + B ( − 3 + 3 ) = − A -3 = A(-3+2) + B(-3+3) = -A − 3 = A ( − 3 + 2 ) + B ( − 3 + 3 ) = − A , so A = 3 A = 3 A = 3 . If x = − 2 x = -2 x = − 2 , then − 2 = A ( − 2 + 2 ) + B ( − 2 + 3 ) = B -2 = A(-2+2) + B(-2+3) = B − 2 = A ( − 2 + 2 ) + B ( − 2 + 3 ) = B , so B = − 2 B = -2 B = − 2 . Therefore, x ( x + 3 ) ( x + 2 ) = 3 x + 3 − 2 x + 2 \frac{x}{(x+3)(x+2)} = \frac{3}{x+3} - \frac{2}{x+2} ( x + 3 ) ( x + 2 ) x = x + 3 3 − x + 2 2 .
ii. Express 2 x 2 + 6 x + 1 x ( x + 1 ) \frac{2x^2+6x+1}{x(x+1)} x ( x + 1 ) 2 x 2 + 6 x + 1 in partial fractions. Since the degree of the numerator is equal to the degree of the denominator, we perform polynomial long division first.
2 x 2 + 6 x + 1 x ( x + 1 ) = 2 x 2 + 6 x + 1 x 2 + x = 2 + 4 x + 1 x ( x + 1 ) \frac{2x^2+6x+1}{x(x+1)} = \frac{2x^2+6x+1}{x^2+x} = 2 + \frac{4x+1}{x(x+1)} x ( x + 1 ) 2 x 2 + 6 x + 1 = x 2 + x 2 x 2 + 6 x + 1 = 2 + x ( x + 1 ) 4 x + 1 . Now we express 4 x + 1 x ( x + 1 ) \frac{4x+1}{x(x+1)} x ( x + 1 ) 4 x + 1 in partial fractions. 4 x + 1 x ( x + 1 ) = C x + D x + 1 \frac{4x+1}{x(x+1)} = \frac{C}{x} + \frac{D}{x+1} x ( x + 1 ) 4 x + 1 = x C + x + 1 D . Multiplying both sides by x ( x + 1 ) x(x+1) x ( x + 1 ) , we get 4 x + 1 = C ( x + 1 ) + D x 4x+1 = C(x+1) + Dx 4 x + 1 = C ( x + 1 ) + D x . If x = 0 x = 0 x = 0 , then 1 = C ( 0 + 1 ) + D ( 0 ) = C 1 = C(0+1) + D(0) = C 1 = C ( 0 + 1 ) + D ( 0 ) = C , so C = 1 C = 1 C = 1 . If x = − 1 x = -1 x = − 1 , then − 4 + 1 = C ( − 1 + 1 ) + D ( − 1 ) = − D -4+1 = C(-1+1) + D(-1) = -D − 4 + 1 = C ( − 1 + 1 ) + D ( − 1 ) = − D , so − 3 = − D -3 = -D − 3 = − D , which means D = 3 D = 3 D = 3 . Therefore, 4 x + 1 x ( x + 1 ) = 1 x + 3 x + 1 \frac{4x+1}{x(x+1)} = \frac{1}{x} + \frac{3}{x+1} x ( x + 1 ) 4 x + 1 = x 1 + x + 1 3 . So, 2 x 2 + 6 x + 1 x ( x + 1 ) = 2 + 1 x + 3 x + 1 \frac{2x^2+6x+1}{x(x+1)} = 2 + \frac{1}{x} + \frac{3}{x+1} x ( x + 1 ) 2 x 2 + 6 x + 1 = 2 + x 1 + x + 1 3 .