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Найти точки экстремума и иятервалы монотонкости функции: y=3x2+x3 y=\sqrt{3 x^{2}+x^{3}}

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Q. Найти точки экстремума и иятервалы монотонкости функции: y=3x2+x3 y=\sqrt{3 x^{2}+x^{3}}
  1. Find Derivative: To find the points of extremum and intervals of monotonicity, we first need to find the derivative of the function.\newliney=3x2+x3 y=\sqrt{3 x^{2}+x^{3}} \newlineLet's find the derivative using the chain rule.\newliney=123x2+x3(6x+3x2) y' = \frac{1}{2\sqrt{3 x^{2}+x^{3}}} \cdot (6x + 3x^2) \newlineSimplify the derivative.\newliney=3x(2+x)23x2+x3 y' = \frac{3x(2+x)}{2\sqrt{3 x^{2}+x^{3}}}
  2. Find Critical Points: Next, we need to find the critical points by setting the derivative equal to zero and solving for x.\newline3x(2+x)23x2+x3=0 \frac{3x(2+x)}{2\sqrt{3 x^{2}+x^{3}}} = 0 \newlineThis equation is zero when the numerator is zero, so we set 3x(2+x)=0 3x(2+x) = 0 and solve for x.\newline3x=0or2+x=0 3x = 0 \quad \text{or} \quad 2+x = 0 \newlinex=0orx=2 x = 0 \quad \text{or} \quad x = -2
  3. Consider Domain: We must also consider the domain of the original function, as the derivative must exist within this domain. The function y=3x2+x3 y=\sqrt{3 x^{2}+x^{3}} is defined for all x where 3x2+x30 3 x^{2}+x^{3} \geq 0 . Factoring out x2 x^2 , we get x2(3+x)0 x^2(3+x) \geq 0 . This inequality holds for x3 x \leq -3 and x0 x \geq 0 . Therefore, the critical point at x=2 x = -2 is not in the domain of the function, and we only consider x=0 x = 0 .
  4. Test Intervals: Now we need to test the intervals around the critical point x=0 x = 0 to determine the intervals of monotonicity. We choose test points x=1 x = -1 (which is not in the domain, so we ignore it) and x=1 x = 1 .\newlineFor x=1 x = 1 :\newliney=3(1)(2+1)23(1)2+(1)3=926>0 y' = \frac{3(1)(2+1)}{2\sqrt{3(1)^{2}+(1)^{3}}} = \frac{9}{2\sqrt{6}} > 0 \newlineSince the derivative is positive, the function is increasing on the interval (0,) (0, \infty) .
  5. Identify Minimum Point: For x=3 x = -3 (which is at the boundary of the domain), we notice that the function y=3x2+x3 y=\sqrt{3 x^{2}+x^{3}} simplifies to y=x2(3+x) y=\sqrt{x^2(3+x)} , which is zero at x=3 x = -3 . Since the function is zero and then starts increasing after x=0 x = 0 , we can say that x=3 x = -3 is a minimum point.
  6. Summary: To summarize, the function has a minimum point at x=3 x = -3 and is increasing on the interval (0,) (0, \infty) . There are no maximum points since the function does not decrease after any point.

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