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Use the formula for the surface area of revolution, which requires dy/dx. So find dy/dx = sinh(x) and substitute dy/dx and y into the formula with the limits provided in the question (2 and 6). Then evalu...

It is not just trial and error, as this will eat away time in the exam. if you can't see it straight away then you need to consider some things. for example a common question might be find the integral of...

to find the derivative, we can first make this easier to visualise. Say a second variable, y, is included to make this become y = arcsinx. now if we sin both sides, we get siny = x. we already know the de...

Using the question, first use de Moivre's theorem to say (cos x + i sin x)^5 = cos 5x + isin 5x. Now we can use a binomial expansion on the RHS to say 

cos 5x + isin 5x = cos⁵ x + 5i cos...