The answer should be y=-1/7x
-43 - 4r = 3 - 27r
Add 27r to both sides. -43 - 4r + 27r = 3 -27r + 27r or -43 + 23r = 3
Add 43 to both sides. -43 + 43 +23r = 3 + 43 or 23r = 46.
Divide both sides by 23 to get r by itself. 23r / 23 = 46 / 23 or r = 2
r = 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.
