(a) Solve 8 − x 2 + x = 2 5 x − 1 8^{-x^2 + x} = 2^{5x-1} 8 − x 2 + x = 2 5 x − 1 . First, rewrite 8 as 2 3 2^3 2 3 : ( 2 3 ) − x 2 + x = 2 5 x − 1 (2^3)^{-x^2 + x} = 2^{5x-1} ( 2 3 ) − x 2 + x = 2 5 x − 1 . Then, using the property ( a b ) c = a b c (a^b)^c = a^{bc} ( a b ) c = a b c : 2 3 ( − x 2 + x ) = 2 5 x − 1 2^{3(-x^2 + x)} = 2^{5x-1} 2 3 ( − x 2 + x ) = 2 5 x − 1 . Since the bases are equal, we can equate the exponents:
3 ( − x 2 + x ) = 5 x − 1 3(-x^2 + x) = 5x - 1 3 ( − x 2 + x ) = 5 x − 1 − 3 x 2 + 3 x = 5 x − 1 -3x^2 + 3x = 5x - 1 − 3 x 2 + 3 x = 5 x − 1 3 x 2 + 2 x − 1 = 0 3x^2 + 2x - 1 = 0 3 x 2 + 2 x − 1 = 0 We can factor this quadratic equation as:
( 3 x − 1 ) ( x + 1 ) = 0 (3x - 1)(x + 1) = 0 ( 3 x − 1 ) ( x + 1 ) = 0 Therefore, 3 x − 1 = 0 3x - 1 = 0 3 x − 1 = 0 or x + 1 = 0 x + 1 = 0 x + 1 = 0 . x = 1 3 x = \frac{1}{3} x = 3 1 or x = − 1 x = -1 x = − 1 .
(b) Solve l o g a ( 2 p + 1 ) + l o g a ( 3 p − 10 ) = l o g a ( 11 p ) log_a(2p+1) + log_a(3p-10) = log_a(11p) l o g a ( 2 p + 1 ) + l o g a ( 3 p − 10 ) = l o g a ( 11 p ) for p > 0 p>0 p > 0 . Using the logarithm property l o g a ( b ) + l o g a ( c ) = l o g a ( b c ) log_a(b) + log_a(c) = log_a(bc) l o g a ( b ) + l o g a ( c ) = l o g a ( b c ) : l o g a ( ( 2 p + 1 ) ( 3 p − 10 ) ) = l o g a ( 11 p ) log_a((2p+1)(3p-10)) = log_a(11p) l o g a (( 2 p + 1 ) ( 3 p − 10 )) = l o g a ( 11 p ) Since the logarithms have the same base, we can equate the arguments:
( 2 p + 1 ) ( 3 p − 10 ) = 11 p (2p+1)(3p-10) = 11p ( 2 p + 1 ) ( 3 p − 10 ) = 11 p 6 p 2 − 20 p + 3 p − 10 = 11 p 6p^2 - 20p + 3p - 10 = 11p 6 p 2 − 20 p + 3 p − 10 = 11 p 6 p 2 − 17 p − 10 = 11 p 6p^2 - 17p - 10 = 11p 6 p 2 − 17 p − 10 = 11 p 6 p 2 − 28 p − 10 = 0 6p^2 - 28p - 10 = 0 6 p 2 − 28 p − 10 = 0 Divide the equation by 2:
3 p 2 − 14 p − 5 = 0 3p^2 - 14p - 5 = 0 3 p 2 − 14 p − 5 = 0 We can factor this quadratic equation as:
( 3 p + 1 ) ( p − 5 ) = 0 (3p + 1)(p - 5) = 0 ( 3 p + 1 ) ( p − 5 ) = 0 Therefore, 3 p + 1 = 0 3p + 1 = 0 3 p + 1 = 0 or p − 5 = 0 p - 5 = 0 p − 5 = 0 . p = − 1 3 p = -\frac{1}{3} p = − 3 1 or p = 5 p = 5 p = 5 . Since p > 0 p>0 p > 0 , we discard the solution p = − 1 3 p = -\frac{1}{3} p = − 3 1 . Also we have the condition that 3 p − 10 > 0 3p-10>0 3 p − 10 > 0 so p > 10 3 p > \frac{10}{3} p > 3 10 . Since 5 > 10 3 5 > \frac{10}{3} 5 > 3 10 , p = 5 p=5 p = 5 is a valid solution.
(c) Solve l o g 2 ( x ) − 3 + l o g 2 ( x + 3 ) = 0 log_2(x) - 3 + log_2(x+3) = 0 l o g 2 ( x ) − 3 + l o g 2 ( x + 3 ) = 0 . Using the logarithm property l o g a ( b ) + l o g a ( c ) = l o g a ( b c ) log_a(b) + log_a(c) = log_a(bc) l o g a ( b ) + l o g a ( c ) = l o g a ( b c ) : l o g 2 ( x ( x + 3 ) ) − 3 = 0 log_2(x(x+3)) - 3 = 0 l o g 2 ( x ( x + 3 )) − 3 = 0 l o g 2 ( x ( x + 3 ) ) = 3 log_2(x(x+3)) = 3 l o g 2 ( x ( x + 3 )) = 3 Using the property l o g a ( b ) = c ⟺ a c = b log_a(b) = c \iff a^c = b l o g a ( b ) = c ⟺ a c = b : x ( x + 3 ) = 2 3 x(x+3) = 2^3 x ( x + 3 ) = 2 3 x 2 + 3 x = 8 x^2 + 3x = 8 x 2 + 3 x = 8 x 2 + 3 x − 8 = 0 x^2 + 3x - 8 = 0 x 2 + 3 x − 8 = 0 Using the quadratic formula x = − b ± b 2 − 4 a c 2 a x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} x = 2 a − b ± b 2 − 4 a c : x = − 3 ± 3 2 − 4 ( 1 ) ( − 8 ) 2 ( 1 ) x = \frac{-3 \pm \sqrt{3^2 - 4(1)(-8)}}{2(1)} x = 2 ( 1 ) − 3 ± 3 2 − 4 ( 1 ) ( − 8 ) x = − 3 ± 9 + 32 2 x = \frac{-3 \pm \sqrt{9 + 32}}{2} x = 2 − 3 ± 9 + 32 x = − 3 ± 41 2 x = \frac{-3 \pm \sqrt{41}}{2} x = 2 − 3 ± 41 Since we must have x > 0 x>0 x > 0 , we discard the negative root. Thus x = − 3 + 41 2 x = \frac{-3 + \sqrt{41}}{2} x = 2 − 3 + 41