If y 3 cos x 3 find dy dx when x 3 2 - JAMB Mathematics 2004 Question
If y = 3 cos(x/3), find dy/dx when x = (3π/2)
A
1
B
-3
C
2
D
-1
correct option: d
y = 3cos(x/3)
dy/dx = 3x(1/3)x - sin (x/3)
= - sin x/3
But x = 3π/2 ∴ -sin(x/3) = -sin(3π/6)
= -sin (3 * 180)/6
= - sin 90
= -1
dy/dx = 3x(1/3)x - sin (x/3)
= - sin x/3
But x = 3π/2 ∴ -sin(x/3) = -sin(3π/6)
= -sin (3 * 180)/6
= - sin 90
= -1
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