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Express 3 cos θ + 4 sin θ in the form R cos(θ – α), where R and α are constants, R > 0 and 0 < α < 90°.

To find the value of R, use Pythagoras's Theorem using the coeffecients of cos θ and sin θ. The correct answer should be R=5. Expand the expression R cos(θ – α). Equate the expanded expression with 3 cos θ +...
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Answered by Anahita G. Maths tutor
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How do I use the product rule for differentiation?

The product rule is a rule for differentiating products of expressions, i.e. 2 expressions multiplied together. The rule is: if y=A B, then dy/dx=A dB/dx +B*dA/dx. This can be remembered as &quot;Write down ...
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Answered by Thomas E. Maths tutor
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How do I evaluate composite functions?

Suppose you have 2 functions: f(x) = 3x 2 , g(x) = log 3 (x). These are arbitrary, any functions would work. Evaluate f(g(x)): let y = log 3 (x) ( = g(x) ), then f(g(x)) = f(y) = 3y 2 = 3[log 3 (x)] 2 . The ...
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Answered by Seb G. Maths tutor
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How do I differentiate implicitly?

The most important thing to remember when differentiating implicitly is that y is a function of x. Rewriting y as y(x) often makes it much clearer. For example, evaluate d/dx (y 2 ): using the aforementioned...
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Answered by Seb G. Maths tutor
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A cup of coffee is cooling down in a room following the equation x = 15 + 70e^(-t/40). Find the rate at which the temperature is decreasing when the coffee cools to 60°C.

First, we need to find the value of t when x = 6p°C. We are told that after t minutes the temperature, x, will be 60°C; so we can insert 60 into the equation for x: 60 = 15 + 70e^(-t/40) Secondly, we can rea...
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Answered by Nathan A. Maths tutor
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