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Sia

Question
Math
Posted 11 months ago
nice!
4 The curve y=e4xtanxy=\mathrm{e}^{-4 x} \tan x has two stationary points in the interval 0x<12π0 \leqslant x<\frac{1}{2} \pi.
(a) Obtain an expression for dy dx\frac{\mathrm{d} y}{\mathrm{~d} x} and show it can be written in the form sec2x(a+bsin2x)e4x\sec ^{2} x(a+b \sin 2 x) \mathrm{e}^{-4 x}, where aa and bb are constants.
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Answer from Sia
Posted 11 months ago
Solution by Steps
step 1
To find the derivative of y=e4xtan(x) y = e^{-4x} \tan(x) , we use the product rule which states that (fg)=fg+fg (fg)' = f'g + fg'
step 2
The derivative of e4x e^{-4x} is 4e4x -4e^{-4x} , and the derivative of tan(x) \tan(x) is sec2(x) \sec^2(x)
step 3
Applying the product rule, we get dydx=e4xsec2(x)4e4xtan(x) \frac{dy}{dx} = e^{-4x} \sec^2(x) - 4e^{-4x} \tan(x)
step 4
We can express tan(x) \tan(x) as sin(2x)2 \frac{\sin(2x)}{2} since tan(x)=sin(2x)2cos(x) \tan(x) = \frac{\sin(2x)}{2\cos(x)}
step 5
Substituting tan(x) \tan(x) into the derivative, we get dydx=e4xsec2(x)2e4xsin(2x) \frac{dy}{dx} = e^{-4x} \sec^2(x) - 2e^{-4x} \sin(2x)
step 6
We can factor out e4xsec2(x) e^{-4x} \sec^2(x) to write the derivative in the form sec2(x)(a+bsin(2x))e4x \sec^2(x)(a + b\sin(2x))e^{-4x}
step 7
Comparing the expression to the required form, we identify a=1 a = 1 and b=2 b = -2
Answer
dydx=sec2(x)(12sin(2x))e4x \frac{dy}{dx} = \sec^2(x)(1 - 2\sin(2x))e^{-4x} , where a=1 a = 1 and b=2 b = -2 .
Key Concept
Product Rule and Trigonometric Identities
Explanation
To find the derivative of a product of functions, we use the product rule. Additionally, trigonometric identities help us to express the derivative in a specific form, allowing us to identify the constants a a and b b .

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