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The curve C has equation y = (2x - 3)^{5} The point P lies on C and has coordinates (w, -32) - Edexcel - A-Level Maths Pure - Question 23 - 2013 - Paper 1

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The curve C has equation y = (2x - 3)^{5} The point P lies on C and has coordinates (w, -32). Find a) the value of w; b) the equation of the tangent to C at the ... show full transcript

Worked Solution & Example Answer:The curve C has equation y = (2x - 3)^{5} The point P lies on C and has coordinates (w, -32) - Edexcel - A-Level Maths Pure - Question 23 - 2013 - Paper 1

Step 1

Find the value of w

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Answer

To find the value of w, we substitute y = -32 into the curve equation:

32=(2w3)5-32 = (2w - 3)^{5}

Next, we take the fifth root of both sides:

2w3=(32)1/52w - 3 = (-32)^{1/5}

Recognizing that (32)1/5(-32)^{1/5} is -2, we solve for w:

2w3=22w - 3 = -2 2w=12w = 1 w=12w = \frac{1}{2}

Step 2

Find the equation of the tangent to C at the point P

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Answer

To find the equation of the tangent at point P, we first need to differentiate the curve:

y=(2x3)5y = (2x - 3)^{5}

Using the chain rule:

dydx=5(2x3)42=10(2x3)4\frac{dy}{dx} = 5(2x - 3)^{4} \cdot 2 = 10(2x - 3)^{4}

Now we evaluate the derivative at x = \frac{1}{2}:

dydxx=12=10(2(12)3)4=10(2)4=1016=160\frac{dy}{dx} \Big|_{x=\frac{1}{2}} = 10(2(\frac{1}{2}) - 3)^{4} = 10(-2)^{4} = 10 \cdot 16 = 160

Thus, the gradient of the tangent at P is 160. Now, we can write the tangent equation using point-slope form:

y(32)=160(x12)y - (-32) = 160(x - \frac{1}{2})

Simplifying this gives:

y+32=160x80y + 32 = 160x - 80 y=160x112y = 160x - 112

Therefore, the equation of the tangent is:

y=160x112y = 160x - 112

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