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Find an equation for a sinusoidal function that has period 2Ο€2\pi, amplitude 11, and contains the point (0,βˆ’1)(0, -1). Write your answer in the form f(x)=Acos⁑(Bx+C)+Df(x)=A\cos(Bx+C)+D, where AA, BB, CC, and DD are real numbers.

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Q. Find an equation for a sinusoidal function that has period 2Ο€2\pi, amplitude 11, and contains the point (0,βˆ’1)(0, -1). Write your answer in the form f(x)=Acos⁑(Bx+C)+Df(x)=A\cos(Bx+C)+D, where AA, BB, CC, and DD are real numbers.
  1. Period Calculation: We are given the period of the sinusoidal function as 2Ο€2\pi. To find the value of BB, which affects the period of the cosine function, we use the formula for the period of a cosine function, which is (2Ο€)/B(2\pi)/B.
  2. Calculation of B: Since the period is 2Ο€2\pi, we set up the equation (2Ο€)/B=2Ο€(2\pi)/B = 2\pi and solve for B.\newline(2Ο€)/B=2Ο€(2\pi)/B = 2\pi\newlineB=(2Ο€)/(2Ο€)B = (2\pi)/(2\pi)\newlineB=1B = 1
  3. Amplitude and Shift: Next, we know the amplitude AA is given as 11. This means the function will have a maximum value of 11 and a minimum value of βˆ’1-1. Since the point (0,βˆ’1)(0, -1) is on the graph, this indicates that the cosine function must be shifted vertically or horizontally to pass through this point.
  4. General Cosine Function: The general form of the cosine function is f(x)=Acos⁑(Bx+C)+Df(x) = A\cos(Bx + C) + D. Since we have A=1A = 1 and B=1B = 1, we can substitute these values into the equation to get f(x)=cos⁑(x+C)+Df(x) = \cos(x + C) + D.
  5. Determining Values of C and D: Now we need to determine the values of C and D. Since the function passes through the point (0,βˆ’1)(0, -1), we can substitute x=0x = 0 and f(x)=βˆ’1f(x) = -1 into the equation to find D.\newlineβˆ’1=cos⁑(0+C)+D-1 = \cos(0 + C) + D\newlineSince cos⁑(0)=1\cos(0) = 1 for any value of C, we have:\newlineβˆ’1=1+D-1 = 1 + D\newlineD=βˆ’1βˆ’1D = -1 - 1\newlineD=βˆ’2D = -2
  6. Correction for Value of D: However, we have made a mistake in the previous step. The amplitude of the function is 11, so the maximum and minimum values of the function are 11 and βˆ’1-1, respectively. Since the point (0,βˆ’1)(0, -1) is on the graph and the amplitude is 11, this means that the cosine function is at its minimum value when x=0x = 0. Therefore, the value of DD should be βˆ’1-1, not βˆ’2-2, because the vertical shift DD must bring the minimum value of the cosine function down to βˆ’1-1.

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