Q. Determine the values of x for which64cosh4x−64cosh2x−9=0Give your answers in the form qln2 where q is rational and in simplest form.
Substitution Simplification: Let's start by simplifying the equation using a substitution. Let u=cosh2(x). The equation then becomes 64u2−64u−9=0.
Quadratic Equation Solution: Next, we'll solve the quadratic equation64u2−64u−9=0. Using the quadratic formula, u=2a−b±b2−4ac, where a=64, b=−64, and c=−9.
Root Calculation: Plugging in the values, we get u=2⋅6464±(−64)2−4⋅64⋅(−9). Simplifying inside the square root: u=12864±4096+2304.
Validating Solution: Further simplifying, u=(64±6400)/128=(64±80)/128. This gives us u=144/128 or u=−16/128, which simplifies to u=9/8 or u=−1/8.
Finding x: Since cosh2(x) cannot be negative, we discard u=−81. We only consider u=89. Now, we need to find x such that cosh2(x)=89.
Square Root Calculation: Taking the square root on both sides, cosh(x)=89=83=432.
Equation Rearrangement: Using the definition of cosh(x)=2ex+e−x, we set up the equation 2ex+e−x=432. Multiplying through by 2 and rearranging, we get ex+e−x=232.
Quadratic Equation Solution: Solving for ex, let y=ex. Then y+y1=232. Multiplying through by y, we get y2−(232)y+1=0.
Quadratic Equation Solution: Solving for ex, let y=ex. Then y+y1=232. Multiplying through by y, we get y2−(232)y+1=0. Solving this quadratic equation for y, we use the quadratic formula again: y=2(232)±(232)2−4.
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