Find the maxima, minima, and saddle points of the function f(x,y) = (x2 - 1)(x+2).
|Mathematics
Find the maxima, minima, and saddle points of the function f(x,y) = (x2 - 1)(x+2).
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Answer
x^3 + 2x^2 - x - 2$.
To find the maxima, minima, and saddle points of the function f(x,y)=(x2−1)(x+2), we first observe that the function only depends on x. We can write it as f(x)=x3+2x2−x−2.
Step 1: Find the first partial derivatives and set them to zero to find critical points.
The given function is f(x,y)=x3+2x2−x−2.
The partial derivative with respect to x is:
fx=∂x∂(x3+2x2−x−2)=3x2+4x−1
The partial derivative with respect to y is:
fy=∂y∂(x3+2x2−x−2)=0
Set fx=0 and fy=0:
3x2+4x−1=0
0=0
From equation (1), we use the quadratic formula x=2a−b±b2−4ac to find the values of x:
x=2(3)−4±42−4(3)(−1)x=6−4±16+12x=6−4±28x=6−4±27x=3−2±7
The critical points are lines where x=3−2+7 and x=3−2−7.
Step 2: Find the second partial derivatives.
fxx=∂x∂(3x2+4x−1)=6x+4fyy=∂y∂(0)=0fxy=∂y∂(3x2+4x−1)=0
Step 3: Calculate the discriminant D(x,y)=fxxfyy−(fxy)2.
D(x,y)=(6x+4)(0)−(0)2=0
Since D(x,y)=0, the Second Derivative Test is inconclusive. However, since the function only depends on x, we can analyze the behavior of f(x) using its second derivative f′′(x)=fxx(x).
Step 4: Classify the critical points using fxx.
For x1=3−2+7:
fxx(3−2+7)=6(3−2+7)+4fxx(3−2+7)=2(−2+7)+4fxx(3−2+7)=−4+27+4=27
Since 27>0, the critical line x=3−2+7 corresponds to a local minimum.
For x2=3−2−7:
fxx(3−2−7)=6(3−2−7)+4fxx(3−2−7)=2(−2−7)+4fxx(3−2−7)=−4−27+4=−27
Since −27<0, the critical line x=3−2−7 corresponds to a local maximum.
Step 5: Calculate the function values at these critical lines.
At the critical points, 3x2+4x−1=0, which means 3x2=1−4x.
We can simplify f(x)=x3+2x2−x−2 using this relation:
f(x)=x(x2)+2x2−x−2
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This mathematics problem involves applying core mathematical principles and formulas. Below you will find a complete step-by-step solution with detailed explanations for each step, helping you understand not just the answer but the method behind it.
ScanSolve AI Answer
To find the maxima, minima, and saddle points of the function f(x,y) = (x^2 - 1)(x+2), we first observe that the function only depends on x. We can write it as f(x) = x^3 + 2x^2 - x - 2. Step 1: Find the first partial derivatives and set them to zero to find critical points. The given function is f(x,y) = x^3 + 2x^2 - x - 2. The partial derivative with respect to x is: f_x = ()/( x)(x^3 + 2x^2 - x - 2) = 3x^2 + 4x - 1 The partial derivative with respect to y is: f_y = ()/( y)(x^3 + 2x^2 - x - 2) = 0 Set f_x = 0 and f_y = 0: 1) 3x^2 + 4x - 1 = 0 2) 0 = 0 From equation (1), we use the quadratic formula x = -b ± sqrt(b^2 - 4ac)2a to find the values of x: x = -4 ± sqrt(4^2 - 4(3)(-1))2(3) x = -4 ± sqrt(16 + 12)6 x = -4 ± sqrt(28)6 x = -4 ± 2sqrt(7)6 x = -2 ± sqrt(7)3 The critical points are lines where x = -2 + sqrt(7)3 and x = -2 - sqrt(7)3. Step 2: Find the second partial derivatives. f_xx = ()/( x)(3x^2 + 4x - 1) = 6x + 4 f_yy = ()/( y)(0) = 0 f_xy = ()/( y)(3x^2 + 4x - 1) = 0 Step 3: Calculate the discriminant D(x,y) = f_xxf_yy - (f_xy)^2. D(x,y) = (6x + 4)(0) - (0)^2 = 0 Since D(x,y) = 0, the Second Derivative Test is inconclusive. However, since the function only depends on x, we can analyze the behavior of f(x) using its second derivative f''(x) = f_xx(x). Step 4: Classify the critical points using f_xx. For x_1 = -2 + sqrt(7)3: f_xx(-2 + sqrt(7)3) = 6(-2 + sqrt(7)3) + 4 f_xx(-2 + sqrt(7)3) = 2(-2 + sqrt(7)) + 4 f_xx(-2 + sqrt(7)3) = -4 + 2sqrt(7) + 4 = 2sqrt(7) Since 2sqrt(7) > 0, the critical line x = -2 + sqrt(7)3 corresponds to a local minimum. For x_2 = -2 - sqrt(7)3: f_xx(-2 - sqrt(7)3) = 6(-2 - sqrt(7)3) + 4 f_xx(-2 - sqrt(7)3) = 2(-2 - sqrt(7)) + 4 f_xx(-2 - sqrt(7)3) = -4 - 2sqrt(7) + 4 = -2sqrt(7) Since -2sqrt(7) < 0, the critical line x = -2 - sqrt(7)3 corresponds to a local maximum. Step 5: Calculate the function values at these critical lines. At the critical points, 3x^2 + 4x - 1 = 0, which means 3x^2 = 1 - 4x. We can simplify f(x) = x^3 + 2x^2 - x - 2 using this relation: f(x) = x(x^2) + 2x^2 - x - 2 f(x