Q. Найти точки экстремума и иятервалы монотонкости функции: y=3x2+x3
Find Derivative: To find the points of extremum and intervals of monotonicity, we first need to find the derivative of the function.y=3x2+x3Let's find the derivative using the chain rule.y′=23x2+x31⋅(6x+3x2)Simplify the derivative.y′=23x2+x33x(2+x)
Find Critical Points: Next, we need to find the critical points by setting the derivative equal to zero and solving for x.23x2+x33x(2+x)=0This equation is zero when the numerator is zero, so we set 3x(2+x)=0 and solve for x.3x=0or2+x=0x=0orx=−2
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 is defined for all x where 3x2+x3≥0. Factoring out x2, we get x2(3+x)≥0. This inequality holds for x≤−3 and x≥0. Therefore, the critical point at x=−2 is not in the domain of the function, and we only consider x=0.
Test Intervals: Now we need to test the intervals around the critical point x=0 to determine the intervals of monotonicity. We choose test points x=−1 (which is not in the domain, so we ignore it) and x=1.For x=1:y′=23(1)2+(1)33(1)(2+1)=269>0Since the derivative is positive, the function is increasing on the interval (0,∞).
Identify Minimum Point: For x=−3 (which is at the boundary of the domain), we notice that the function y=3x2+x3 simplifies to y=x2(3+x), which is zero at x=−3. Since the function is zero and then starts increasing after x=0, we can say that x=−3 is a minimum point.
Summary: To summarize, the function has a minimum point at x=−3 and is increasing on the interval (0,∞). There are no maximum points since the function does not decrease after any point.
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