Disucss Test Questions - Test:38 QNo:3

1

Manmay kumar Mohanty ·Mar 4 '10 at 7:25

some one tell me the ans. given was -3cos2xsin4x. HOW?

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1

Ajaay Srinivasan ·Mar 4 '10 at 8:14

is dis d ans....................

-6sin(2x)cos_square(2x)

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49

Subhomoy Bakshi ·Mar 4 '10 at 8:24

ohh yea
same answers....[4][3][3]

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39

Pritish Chakraborty ·Mar 4 '10 at 8:25

$ d x d y = 3 c o s 2 (2 x) . (- s i n (2 x)) . 2 = - 6 c o s 2 (2 x) s i n (2 x)$

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1

akshay sharma ·Mar 4 '10 at 8:28

y=cos³ (2x)

dy/dx=3cos²(2x).2sin(2x).2

= -3cos(2x).cos(2X).2sin(2x)

= -3cos(2x)[2sin(2x).cos(2x)]

= -3cos(2x)sin(4x)

thus ans given z absolutely correct.................

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49

Subhomoy Bakshi ·Mar 4 '10 at 8:32

$y = c o s 3 (2 x)$
$\Rightarrow \frac{dy}{dx}=\frac{d}{dx}cos^{3}(2x)$
$\Rightarrow \frac{dy}{dx}=3cos^{2}(2x)[-2sin(2x)]=-3cos(2x)[2sin(2x)cos(2x)]=-3cos(2x)sin(4x)$

any way both the answers are correct!!

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