当x趋近于0时,无穷小量sin3x-3sinx的主部是?
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发布时间:2024-10-11 08:36
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时间:2024-11-13 22:33
f(x) = sin(x),
f(0) = 0,
f'(x) = cos(x), f'(0) = 1,
f''(x) = -sin(x), f''(0) = 0.
f'''(x) = -cos(x), f'''(0) = -1.
f(x) = sin(x) = f(0) + f'(0)(x-0) + f''(0)(x-0)^2/2! + f'''(0)(x-0)^3/3! + o(x^3)
= x - x^3/6 + o(x^3)
sin(3x) = (3x) - (3x)^3/6 + o(x^3)
= 3x - 27x^3/6 + o(x^3)
sin(3x) - 3sin(x) = [3x - 27x^3/6] - 3[x - x^3/6] + o(x^3)
= -24x^3/6 + o(x^3)
= -4x^3 + o(x^3)
x->0时,sin(3x) - 3sin(x)的主部是,-4x^3