Q. Find all critical points of the function f(x)=cos−1(x)+3x for −1<x<1.
Find Derivative and Set Equal: To find the critical points of the function f(x)=cos−1(x)+3x, we need to find the derivative of the function and set it equal to 0.
Calculate Derivative: The derivative of f(x) with respect to x is given by f′(x)=dxd[cos−1(x)]+dxd[3x].
Set Derivative Equal to Zero: Using the chain rule and the fact that the derivative of cos−1(x) is −1−x21, we get f′(x)=−1−x21+3.
Solve for Critical Points: To find the critical points, we set the derivative equal to zero: −1−x21+3=0.
Add 1 to Both Sides: Solving for x, we multiply both sides by 1−x2 to get −1+31−x2=0.
Divide by 3: Next, we add 1 to both sides to obtain 31−x2=1.
Square Both Sides: Dividing both sides by 3 gives us 1−x2=31.
Simplify Equation: Squaring both sides to eliminate the square root gives us 1−x2=(31)2.
Find x Values: This simplifies to 1−x2=91.
Consider Interval: Subtracting 1 from both sides yields −x2=91−1.
Final Critical Points: Simplifying the right side, we get −x2=−98.
Final Critical Points: Simplifying the right side, we get −x2=−98. Dividing by −1, we find x2=98.
Final Critical Points: Simplifying the right side, we get −x2=−98.Dividing by −1, we find x2=98.Taking the square root of both sides, we get x=±98.
Final Critical Points: Simplifying the right side, we get −x2=−98.Dividing by −1, we find x2=98.Taking the square root of both sides, we get x=±98.Simplifying the square root, we find x=±38.
Final Critical Points: Simplifying the right side, we get −x2=−98.Dividing by −1, we find x2=98.Taking the square root of both sides, we get x=±98.Simplifying the square root, we find x=±38.Since we are looking for critical points within the interval -1 < x < 1, we only consider the solutions that fall within this range. The solutions x=±38 are approximately ±0.9428, which are within the interval.
Final Critical Points: Simplifying the right side, we get −x2=−98. Dividing by −1, we find x2=98. Taking the square root of both sides, we get x=±98. Simplifying the square root, we find x=±38. Since we are looking for critical points within the interval -1 < x < 1, we only consider the solutions that fall within this range. The solutions x=±38 are approximately ±0.9428, which are within the interval. Therefore, the critical points of the function f(x)=cos−1(x)+3x for -1 < x < 1 are −10 and −11.
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