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Cosx-3sinx =R(CosxCosa-SinxSina) 1=Rcosa R^2=1^2+3^2  r=(10)^0.5=(approx)3.16 a=1.249 3.16Cos(x+1.249)=4 has no solution as 4<3.16 so as cos(theta) has maximum value of 1, there are no solutions

You should remember that a semi circle is the same as half a circle, therefore the area must be half as well! The formula for the area of a circle is pi r^2. If we use this, the area of our circle = pi x ...

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Using the chain rule: f '(x) = (2x) (3) (x^2 - 1)^2      = 6x(x^2 - 1)^2

The most important thing to do is to practise. Practise speaking in Italian to a native Italian speaker if possible, if not friend, your Mum, your mirror are all also useful. Websites like duolinguo allow...