Y - y1 = m(x - x1)
slope(m) = 2/5
(6,2)....x1 = 6 and y1 = 2
now we sub
y - 2 = 2/5(x - 6)
Im pretty sure the answer is x=-2
F(x) = cos x
f'(x) = -sin x
f''(x) = -cos x
f'''(x) = sin x
f''''(x) = cos x
90/4 = 22 Remainder 2
Therefore, 90th derivative of f(x) = cos x is -cos x.
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