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Write the first four non-zero terms of the power series for 
f(x)=3x cos(2x^(5))-6 about 
x=0

Write the first four non-zero terms of the power series for f(x)=3xcos(2x5)6 f(x)=3 x \cos \left(2 x^{5}\right)-6 about x=0 x=0

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Q. Write the first four non-zero terms of the power series for f(x)=3xcos(2x5)6 f(x)=3 x \cos \left(2 x^{5}\right)-6 about x=0 x=0
  1. Expand Cosine Taylor Series: To find the power series for f(x)=3xcos(2x5)6f(x) = 3x \cos(2x^{5}) - 6 about x=0x = 0, we need to expand the cosine function into its Taylor series and then multiply by 3x3x and subtract 66. The Taylor series for cos(z)\cos(z) about z=0z = 0 is 1z22!+z44!z66!+1 - \frac{z^{2}}{2!} + \frac{z^{4}}{4!} - \frac{z^{6}}{6!} + \ldots, where zz is the input to the cosine function. In our case, z=2x5z = 2x^{5}.
  2. Simplify Series Terms: First, we write down the Taylor series expansion for cos(2x5)\cos(2x^5) about x=0x = 0:cos(2x5)=1(2x5)22!+(2x5)44!(2x5)66!+\cos(2x^5) = 1 - \frac{(2x^5)^2}{2!} + \frac{(2x^5)^4}{4!} - \frac{(2x^5)^6}{6!} + \ldots
  3. Multiply by 3x3x: Now, we simplify the terms of the series: cos(2x5)=14x102+16x202464x30720+\cos(2x^5) = 1 - \frac{4x^{10}}{2} + \frac{16x^{20}}{24} - \frac{64x^{30}}{720} + \ldots
  4. Simplify Coefficients: Next, we multiply each term by 3x3x to get the series for 3xcos(2x5)3x \cos(2x^5):\newline3xcos(2x5)=3x12x112+48x2124192x31720+3x \cos(2x^5) = 3x - \frac{12x^{11}}{2} + \frac{48x^{21}}{24} - \frac{192x^{31}}{720} + \ldots
  5. Subtract 66: We simplify the coefficients:\newline3xcos(2x5)=3x6x11+2x21192720x31+3x \cos(2x^5) = 3x - 6x^{11} + 2x^{21} - \frac{192}{720}x^{31} + \ldots
  6. Identify Non-Zero Term: Now, we subtract 66 from the series to get the final series for f(x)f(x):\newlinef(x)=3xcos(2x5)6=(3x6)6x11+2x21(192720)x31+f(x) = 3x \cos(2x^5) - 6 = (3x - 6) - 6x^{11} + 2x^{21} - \left(\frac{192}{720}\right)x^{31} + \ldots
  7. Final Power Series Terms: We notice that the constant term 6-6 cancels with the constant term from 3x3x when x=0x = 0, so the first non-zero term is actually the term with xx:f(x)=3x6x11+2x21(192720)x31+f(x) = 3x - 6x^{11} + 2x^{21} - \left(\frac{192}{720}\right)x^{31} + \ldots
  8. Final Power Series Terms: We notice that the constant term 6-6 cancels with the constant term from 3x3x when x=0x = 0, so the first non-zero term is actually the term with xx:f(x)=3x6x11+2x21(192720)x31+...f(x) = 3x - 6x^{11} + 2x^{21} - \left(\frac{192}{720}\right)x^{31} + ...The first four non-zero terms of the power series for f(x)f(x) are:3x,6x11,2x21,3x, -6x^{11}, 2x^{21}, and (192720)x31.-\left(\frac{192}{720}\right)x^{31}.

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