Part 1: General Solution of the Wave Equation
Step 1: The given wave equation is a one-dimensional wave equation.
∂t2∂2y=c2∂x2∂2y
The general solution to this equation is given by d'Alembert's formula, which represents the superposition of two waves traveling in opposite directions.
y(x,t)=f(x−ct)+g(x+ct)
where f and g are arbitrary twice-differentiable functions.
The general solution is y(x,t)=f(x−ct)+g(x+ct).
Part 2: Quadratic Function Analysis
Given F(x)=ax2+bx+c and F(x−1)+F(x+1)=3x2+5x−12.
Step 1: Expand F(x−1) and F(x+1).
F(x−1)=a(x−1)2+b(x−1)+c=a(x2−2x+1)+bx−b+c=ax2−2ax+a+bx−b+c
F(x+1)=a(x+1)2+b(x+1)+c=a(x2+2x+1)+bx+b+c=ax2+2ax+a+bx+b+c
Step 2: Sum F(x−1) and F(x+1) and equate coefficients.
F(x−1)+F(x+1)=(ax2−2ax+a+bx−b+c)+(ax2+2ax+a+bx+b+c)
=2ax2+2bx+2a+2c
Comparing this to 3x2+5x−12:
For the x2 term: 2a=3⟹a=23
For the x term: 2b=5⟹b=25
For the constant term: 2a+2c=−12
Substitute a=23: 2(23)+2c=−12⟹3+2c=−12⟹2c=−15⟹c=−215
Step 3: State F(x).
Using the values a=23, b=25, and c=−215:
F(x)=23x2+25x−215
The function is F(x)=23x2+25x−215.
Step 4: Calculate F(2), F(3), F(−2), and F(−3).
- F(2) = \frac{3}{2}(2)^2 + \frac{5}{2}(2) - \frac{15}{2} = \frac{3}{2}(4) + 5 - \frac{15}{2} = 6 + 5 - \frac{15}{2} = 11 - \frac{15}{2} = \frac{22-15}{2} = \frac{7{2}}
- F(3) = \frac{3}{2}(3)^2 + \frac{5}{2}(3) - \frac{15}{2} = \frac{3}{2}(9) + \frac{15}{2} - \frac{15}{2} = \frac{27{2}}
- F(-2) = \frac{3}{2}(-2)^2 + \frac{5}{2}(-2) - \frac{15}{2} = \frac{3}{2}(4) - 5 - \frac{15}{2} = 6 - 5 - \frac{15}{2} = 1 - \frac{15}{2} = \frac{2-15}{2} = -\frac{13{2}}
- F(-3) = \frac{3}{2}(-3)^2 + \frac{5}{2}(-3) - \frac{15}{2} = \frac{3}{2}(9) - \frac{15}{2} - \frac{15}{2} = \frac{27}{2} - \frac{30}{2} = -\frac{3{2}}
Step 5: Determine if F(x) has a minimum or maximum and find its coordinates.
Since the coefficient of x2 is a=23, which is positive (a>0), the parabola opens upwards. Therefore, F(x) has a minimum value.
The x-coordinate of the vertex (the minimum point) is given by x=−2ab.
x=−2(3/2)5/2=−35/2=−65
Now, substitute this x-value back into F(x) to find the y-coordinate (the minimum value):
F(−65)=23(−65)2+25(−65)−215
=23(3625)−1225−215
=2425−2450−24180
=2425−50−180=24−205
The function F(x) has a minimum value. The coordinates of the minimum point are (−65,−24205).
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